Christmas is one of the biggest days on the NBA calendar.

We have a slate of five games and a great opportunity to evaluate many of the league's top title contenders in awesome matchups. But each of the 10 teams playing on Wednesday -- beginning at noon ET on ESPN and the ESPN App -- is facing at least one big question affecting its short- and long-term trajectories.

Let's dive into some of those questions facing this batch of Christmas squads and try to find a few answers.

LISTEN: Christmasketball: NBA Christmas Day Preview

Boston Celtics

One big question: Are they real Finals contenders?

Somehow, despite losing both Al Horford and Kyrie Irving in free agency, the Celtics look better than they did last season.

Kemba Walker is a great fit with this roster, and Boston currently ranks third in the league in net rating. The Celtics are one of just four teams to boast both a top-10 offense and a top-10 defense. (The others -- Milwaukee and both Los Angeles teams -- also play on Christmas.)

The Celtics have great young talent on the wings and good coaching, and their stats scream contender status, but here's the thing: Their bigs might not be good enough. The battle for the East will be won and lost in the paint, and if there's one glaring weakness looming on this roster it's the state of the frontcourt.

Can the Celtics' big men match up against the ferocious interior forces in the East? Can Daniel Theis, Robert Williams and Enes Kanter protect the paint against interior monsters such as Giannis Antetokounmpo and Joel Embiid during a playoff series?

I'm skeptical. The Celtics are 0-2 against Philly this year, and Embiid torched Boston with 38 points and 13 boards on Dec. 12. Last season, the Celts were blown off the court by Antetokounmpo and the Bucks in the playoffs -- and that was with Horford.

You can't come out of the East without answers for Antetokounmpo and Embiid, and it will be difficult for Boston to upgrade at center while holding on to all of its valuable guards and forwards. The Celtics might be stuck trusting Theis and Kanter down the stretch. Nobody in Philly or Milwaukee is afraid of those dudes.

Watch: Celtics vs. Raptors | Noon ET | ESPN and the ESPN App

Toronto Raptors

One big question: How good is Pascal Siakam?

The future of this team rests largely on that question, but the answer seems to change every year. Siakam -- out indefinitely with a groin injury -- has made the leap at least two times now. The reigning Most Improved Player is still improving at a rapid clip, and while Raptors fans should be ecstatic about that, the emerging star still needs to refine a few things.

Siakam is scoring 25.1 points per game, up from 16.9 last season, but his efficiency is way down, especially inside the arc. Some drop in efficiency should have been expected as Siakam became the centerpiece of Toronto's offense, upping his usage rate from 20.5% to 29.3%. But this is pretty drastic:

• Last season, Siakam made 60.2% of his 9.1 2-point tries per game

• This season, he's making 48.6% of his 14.1 2-pointers

That huge drop is due to two factors: atrocious midrange/floater numbers and extra attention from defenders.

Consider this Christmas matchup: Last season, as Boston coach Brad Stevens prepared for the Raptors, his defensive game plan focused on Kawhi Leonard. Siakam was an afterthought. This season, Siakam is the focus, and he sees stronger defenders and more double-teams. His efficiency numbers reflect a young player trying to add a bunch of floaters, pull-ups and post moves to his repertoire, while simultaneously getting hounded by more capable defenders.

The league's brightest superstars blend high usage with high efficiency despite defensive attention, and the next leap for Siakam is clear: He has to recover his shooting numbers with this added load. If he can do that, Toronto will be just fine for years to come.

Watch: Celtics vs. Raptors | Noon ET | ESPN and the ESPN App

Milwaukee Bucks

One big question: Why should we trust this thing?

Fool me once, shame on you. Fool me twice, shame on Bud.

Mike Budenholzer's Bucks have a top-five offense, a top-five defense, the best net rating in the league and the best record. So what? We said all the same things last season, and none of it mattered when Milwaukee crumbled in the Eastern Conference finals.

Once again, Bud has a regular-season juggernaut on his hands, but this time it's Finals or bust. The Bucks are approaching potentially the biggest NBA transaction of 2020 when they extend a supermax contract to Giannis Antetokounmpo. The pressure is on to convince him to stay in Milwaukee for the prime of his career.

The Bucks have something to prove to themselves and to their franchise star. Last spring, Milwaukee lost four straight games after Leonard and the Raptors locked down Antetokounmpo.

The good news is that Leonard moved to Los Angeles, but that doesn't mean getting out of the East this season will be easy. Philly and Boston won't be pushovers, but a trip to the Finals would make that summertime extension much more enticing for the reigning MVP.

Watch: Bucks vs. 76ers | 2:30 p.m. ET | ABC and the ESPN App

Philadelphia 76ers

One big question: Can you build a champion around Embiid and Ben Simmons?

Optimists can point to last season's playoff run and argue that the team was just a few plays away from the Finals, so the answer must be yes. They can also point to an easier path out of the East.

On the other hand, it's unclear if Horford and Josh Richardson can replace JJ Redick and Jimmy Butler in the playoffs. Right now, Philly's offense is on the naughty list. The Sixers have the 15th-best offense in the NBA, and it's particularly awful in fourth quarters, ranking 26th in the final frame. That's a big reason Philly has been a negative fourth-quarter team all season long.

If the Sixers can't execute down the stretch in the regular season, why should we expect them to do so in the postseason?

Last Wednesday, as Butler made his return to Philly, his Heat team emerged with a big win thanks in large part to a clever zone defense, for which Philly's bumbling offense had no answer. It was another failed test for a squad with sky-high expectations.

The other top teams in the East are strong two-way outfits. If Philly can't figure out its offense by the end of the season, the questions about Simmons and Embiid will become much louder than they are now.

Watch: Bucks vs. 76ers | 2:30 p.m. ET | ABC and the ESPN App

Houston Rockets

One big question: Can this team play defense?

When you have Mike D'Antoni as a coach and James Harden at the controls, the questions will never be about offense. Once again, Harden is breaking records and the Rockets' offense is humming along. However, you can't win the West as a one-trick pony. Right now, Houston ranks 16th in defensive efficiency, and that's not good enough.

Last season, the Rockets had an incredible defensive awakening. Their defense ranked No. 25 in the NBA before the All-Star break and then ranked No. 2 overall the rest of the year. So we know they're capable. But will they do it?

If the Rockets enter the playoffs with a solid defense, they are a legitimate threat to win it all. If they don't, they aren't. It's as simple as that. With D'Antoni in the final season of his contract, the next big question for this team might be who is going to be the next coach if Houston falls short again.

Finding a way to acquire Andre Iguodala from the Memphis Grizzlies could make a significant difference here.

Watch: Rockets vs. Warriors | 5 p.m. ET | ABC and the ESPN App

Golden State Warriors

One big question: When will Stephen Curry return?

The Warriors are in hibernation. After a flurry of injuries and defections, they've pushed pause on their dynasty, hoping to resume their dominance next season. In the meantime, they're one of the worst teams in the NBA. They rank 27th in net rating and have lost 12 of their past 16 games.

The state of the Warriors is a reminder of just how star-driven this league is. The defining team of the decade is in shambles following injuries to -- and departures of -- its core stars.

The good news is that eventually two of the best jump-shooters on the planet, Curry and Klay Thompson, will be back in action, and the Warriors will be awesome once again. Until then, it's a campaign for draft position and medical clearances.

Watch: Rockets vs. Warriors | 5 p.m. ET | ABC and the ESPN App

LA Clippers

One big question: Are they better than the Lakers?

There's no question that the Clippers are good, but they're limping into their huge Christmas showdown against the Lakers. They've lost three of their past five games and are barely hanging on to the fourth spot in the West. In the past week, the Nuggets and Rockets have jumped the Clippers in the standings, while the Dallas Mavericks and Utah Jazz are threatening to send LA to the back half of the West playoff picture.

But the Clippers' overall record of 22-10 is deceptive. They are 11-3 when both Kawhi Leonard and Paul George play. Their statistical marks when those guys share the floor are outstanding, and that's what will matter come April, May and June. When Leonard and George are on the court together, the Clippers have a net rating of plus-14.6 points per 100 possessions. Their defensive rating is an absurd 99.6. In other words, they're dominant, folks.

Leonard and George form arguably the best wing combination since Michael Jordan and Scottie Pippen. Both guys are literally among the best in the world on both ends of the court, and the Clippers' less-than-elite overall numbers this season say a lot more about their infamous load management tendencies than they do about their championship chances.

Still, for the Clips to finally get to the promised land, they will have to finally vanquish their mighty crosstown rivals, and the man who has been to Finals in eight of the past nine seasons. Can they do it? We'll get a nice glimpse in this matchup.

Watch: Clippers vs. Lakers | 8 p.m. ET | ABC and the ESPN App

Los Angeles Lakers

One big question: Are they deep enough?

Sunday's home loss to the Nuggets wasn't just the Lakers' biggest margin of defeat all season, it was also the second data point in four days suggesting that this team has a major depth issue. In last Thursday's big showdown in Milwaukee, the Bucks' bench outscored the Lakers' bench 34-4.

Simply put, this team is awesome when LeBron James in on the court and bad when he isn't. The Lakers have major issues when James rests and players such as Quinn Cook, Kyle Kuzma and Rajon Rondo are out there trying to hold the line. It's an uneasy throwback to many of James' Cleveland squads that seemed to barely function whenever James was in a padded folding chair.

The Lakers have a negative net rating when James is off the court (-3.3) because their offense falls apart. Their offensive rating is a very robust 112.9 with James on the floor but a pitiful 102.2 when he's on the bench. For context, the Bulls rank dead last this season with a 103.2 offensive rating. So, yeah ... yuck.

Aside from Anthony Davis, the Lakers are putting up horrid shooting numbers without James on the court. Just how bad are they? Consider these two numbers:

Overall, the Lakers rank third in the NBA by averaging 1.12 points per shot The average shot in the NBA this season is worth 1.07 points.

Now check out the Lakers' most active shooters with LeBron on the bench:

• Anthony Davis: 204 total shots | 1.10 points per shot

• Kyle Kuzma: 91 total shots | 0.92 points per shot

• Quinn Cook: 82 total shots | 0.94 points per shot

• Rajon Rondo: 69 total shots | 0.87 points per shot

• Kentavious Caldwell-Pope: 61 total shots | 0.90 points per shot

• Troy Daniels: 58 total shots | 1.05 points per shot

• Alex Caruso: 57 total shots | 0.91 points per shot

Everyone except AD and Troy Daniels is struggling. There's no doubt this team is a legitimate contender with James on the court, but the Lakers play like a lottery team when their MVP is on the bench.

Watch: Clippers vs. Lakers | 8 p.m. ET | ABC and the ESPN App

New Orleans Pelicans

One big question: When will we see Zion?

The biggest questions for the Pelicans all surround a player who has yet to play a single NBA game: When will we finally see Zion Williamson?

After a promising preseason, Williamson had knee surgery in October and has yet to formally make his NBA debut. Coming into the season, the Pels expected Williamson to spark a potential playoff run, but without him, they have one of the worst records in the league.

This Christmas they should be dreaming more about pingpong balls than playoff seeds, and with that in mind, the focus should turn from game results to possible trades and team-building concepts. Will they trade Jrue Holiday or Redick? Should they re-sign restricted free agent Brandon Ingram? Should they tank the rest of the season?

Few teams have a brighter long-term outlook than the Pelicans, but this season is toast, and the front office needs to start building for next season and beyond -- no matter when Zion is ready to play again.

Watch: Pelicans vs. Nuggets | 10:30 p.m. ET | ESPN and the ESPN App

Denver Nuggets

One big question: Can they get the No. 1 seed?

Nikola Jokic and the Nuggets come into Christmas as the hottest team in the NBA. After beating the Lakers on Sunday and the Suns on Monday, they've won seven in a row and stand alone in second place in the West. They're now within striking distance of the top spot. During the streak, Denver's offense has been on fire, playing through Jokic and punishing teams on the offensive glass.

The top seed is disproportionately important to the Nugs, who are just 7-5 on the road this season and 13-3 at ho-ho-home.

Denver might not have the same superstar shine as the other top teams in the West, but as the San Antonio Spurs have proved six times in the past 20 years, glamour isn't necessary to win the West.

Watch: Pelicans vs. Nuggets | 10:30 p.m. ET | ESPN and the ESPN App