BOSTON -- A year ago, the Boston Celtics entered training camp with championship expectations. This year, it remains to be seen just how good Boston can actually be.

"There are different kinds of questions [this year]," Celtics president of basketball operations Danny Ainge said Saturday before the team's annual open practice here at TD Garden. "I think that last year's questions were more based on, you know, how is it going to gel? There was not a question of how much talent we had.

"This year the question is, 'Are we good enough?'"

That very much is an open question -- particularly due to the departure of Al Horford, who signed as a free agent with the Philadelphia 76ers. That the Celtics were able to replace Kyrie Irving with Kemba Walker meant the loss of Irving -- who declared at this same event a year ago that he intended to re-sign with the Celtics this past summer, only instead to choose to join the rival Brooklyn Nets instead -- was minimized.

Signing Walker using cap space, however, meant that Boston had no way to retain Horford -- or to even find a reasonable replacement for him in free agency. So while Boston expects Walker to seamlessly step into Irving's shoes at the point, and hope Jaylen Brown, Jayson Tatum and Gordon Hayward all take significant strides forward from where they all were last season, how the Celtics go about filling the hole left by Horford, one of the league's most versatile big men, will determine exactly how Ainge's question about his team is answered.

"We had to replace Al Horford, who's a terrific player, and that's hard to do," Ainge said. "He was a 3-point shooter. He was a rim runner. He could defend multiple positions. And so he could do a lot of things on his own, and he was very versatile. But we're going to have to replace him with multiple players. There isn't a player like him that was available."

When asked what he thought would determine whether the Celtics are "good enough," Ainge had a number of things he'll be looking at to see just where Boston's season goes over the next several months.

"Can we make enough shots is always the key. But can we get the stops? Can we rebound the ball well enough? I think those are probably the biggest challenges," he said. "We've been good defensively over the last few years so I worry about our defensive taking a step backwards. We need to have everybody step up on defense."

One thing that would help the Celtics make the transition to a post-Horford world will be Hayward looking like the player he was before the gruesome injury he suffered six games into his first appearance as a Celtic on opening night in Cleveland in 2017.

Like Williams, Hayward has gotten lots of positive reviews for the work he's put in during the offseason, which he chose to spend here in Boston working out at the team's practice facility. But Ainge admitted he's concerned about expectations for Hayward's return performance this season getting ahead of what he can actually produce.

"I think right now there's been a lot of buzz about Gordon and his comeback and I'm worried that it's getting a little out of hand," Ainge said. "Like, I think he's Gordon. He's back to being Gordon. And we're very excited about that. I sometimes worry, like, 'Oh my gosh, they think it's somebody else.' But I'm excited about Gordon.

"Obviously statistics don't matter ... [But] Gordon, depending on how much defensive attention he's getting and who he's on the court with, I think that what I see in Gordon -- and what I've always seen in Gordon when he's been right -- is the ability to score, but also the ability to facilitate and create.

"Gordon is just a good basketball player. He can think, he can pass, he can shoot, he can create, he can defend, he can rebound. I mean, he's a complete player. And we need him to just be that. And we need lots of other guys to play up to their best. And I think we have a chance to be really good."

Saturday was the first time Ainge spoke to the media since training camp began, and one of the few times he's talked since the end of last season, when the Celtics fell far short of their championship expectations with a five-game loss to the Milwaukee Bucks in the Eastern Conference Semifinals -- a finish that laid the groundwork for Irving and and Horford to go elsewhere.

But while others have been reflective about things they learned from last season, Ainge -- now about to enter his fifth decade in NBA life -- said there isn't much he hasn't seen at this point.

"I don't really think I learned anything new," he said with a smile. "There was a lot of things that we hoped wouldn't happen that we were worried could happen. But I've been around the game for 40 years so I think I've seen pretty much everything."

One thing that the way last year played out won't be doing, though, is placing pressure on Ainge's shoulders. When asked at the end of his press conference if he felt any pressure to keep up with the other teams in town -- all of whom have either one a title or been in their respective sport's championship series in the past couple of seasons -- Ainge quickly made it clear he did not.

"I feel more pressure over an eight-foot putt on the 18th hole for a $5 Nassau right now," he said with a smile. "I think that, listen, the championship standard in Boston is well documented. And we all know that. And that's what we love about this [city]. And we love the success of the other teams. And we love the success of the Boston Celtics and what they've done, and the people who have played here and been in uniforms here in our history.

"And so I think that that feeling of high expectations is always good for us."