LAKE BUENA VISTA, Fla. -- As the Philadelphia 76ers prepare to face the Boston Celtics in the first round of the NBA playoffs, Sixers coach Brett Brown said Sunday afternoon that he's contemplating inserting rookie wing Matisse Thybulle into the starting lineup for Game 1 Monday night.

"We're talking a lot about doing different things," Brown said, when asked directly about the possibility of Thybulle going into the starting lineup. "It is being considered."

Brown, of course, demurred when asked directly about whom Thybulle would replace in the starting lineup. He did, however, make it clear Thybulle -- whether he starts or not -- is going to have a big role in the upcoming series between the NBA's oldest rivals.

"Matisse will have a significant role defensively in this series," Brown said.

While Brown wouldn't discuss it, the choice of whom Thybulle would replace in the starting lineup would almost certainly come down to one of two players: point guard Shake Milton, who moved into the starting lineup when Ben Simmons was shifted to power forward full-time when the team arrived in Orlando, Florida, and Al Horford, who moved back into the starting lineup after Simmons was presumably lost for the remainder of the season following knee surgery.

The reason Thybulle, who has been outstanding defensively -- particularly for a rookie -- this season after being drafted 20th overall last year, is being considered for a move into the starting lineup is because the loss of Simmons leaves Philadelphia scrambling to deal with Boston's talented wing players -- specifically All-Star Jayson Tatum.

That's a challenge made more difficult not only by the loss of Simmons, who guarded Tatum on the vast majority of the possessions across the four games between the two teams this season, but because Glenn Robinson III won't be reevaluated for another 7-10 days because of an oblique muscle strain.

"The challenge when you look at all of those gifted wing scorers ... the Ben demise and the Glenn Robinson lack of availability is punishing," Brown said. "And so what it means is you've got to go down to other obvious players -- you're not just going to have [Josh Richardson] and Matisse play 48 minutes -- and so it bleeds into a lot of other things that are the reason you have a team and the group effort, the understanding of some sort of like knowledge of personnel tendencies, the schematic end of a game plan ... it's got to be precise. You don't have the luxury and/or wiggle room of a misstep, of a mistake, a lack of a proper read.

"And so I see it that simply, it's difficult."

Part of what makes it so difficult for Philadelphia to make up for the loss of Simmons is the success he had against Tatum this season. According to Second Spectrum's player tracking data, Simmons guarded Tatum for 155 of the 250 half-court offensive possessions -- and Tatum had an effective field goal percentage of just 28%.

Against all other Sixers defenders over those remaining 95 possessions, that number shot up to 50%. To further emphasize the point: 55 players guarded one player for at least 30 attempted shots this season. Tatum's rate of 0.75 points per shot against Simmons, per Second Spectrum, ranked 54th among those 55 players (with only Utah's Donovan Mitchell's 0.58 points per shot against Denver's Torrey Craig, in another playoff matchup taking place Monday, ranking worse).

Still, in a very small sample size, Thybulle has had some success against Tatum. He has held him to four points on six shots across the 16 possessions that he guarded him. But while Thybulle has often been placed on Kemba Walker during the prior meetings, thanks to Simmons' being available, he said his job defensively doesn't change much whether he's guarding smaller players like Walker or bigger ones like Tatum.

"I mean, it's just really no different," Thybulle said. "Every game I've played, essentially, my job has been to guard the best player, maybe with the exception of like Kawhi [Leonard] and LeBron [James]. But, so really for me this is no different.

"I think the stakes are a little bit higher, and I think we all feel that, but in terms of how I'm approaching it, it's the same way I've had to approach every game. Because every game thus far has been me trying to prove myself to the league, and to our coaches and my teammates. And now, so, it's our team trying to prove ourselves as just being the best."

But whether Thybulle starts or not, one thing is clear: The Sixers know that if they are going to win this series -- especially without Simmons -- it is going to require them to use their size across the board, beginning with Joel Embiid in the paint.

"We're going to use some of our strengths, which is our size and our ability," Sixers forward Tobias Harris said. "We have the most dominant big man in the game. So, using him on the block, letting him go to work."

Then, Harris smiled.

"And that's about all the intel I can give you right now," he said.