BOSTON (CBS) — Kemba Walker’s knee was the big topic for much of the Celtics’ run in the NBA bubble in Orlando over the summer. It’s now going to be a topic to start the 2020-21 season.

After consulting with multiple specialists, Walker received a stem cell injection in his left knee in early October, the team announced on Tuesday. Doctors took stem cells out of Walker’s hip and put them in his knee for the procedure.

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The 30-year-old point guard was put on a 12-week strengthening program after the surgery and is expected to return to on-court activities sometime in the coming weeks. But the Celtics will not update Walker’s game availability until the first week of January, so he’ll be miss the start of the season when things tip off on Dec. 22.

Celtics president of basketball ops. Danny Ainge said Tuesday that he is not very concerned about Walker, and the team is being extra cautious with their starting point guard.

“We are just being very cautious with Kemba. We didn’t have a long enough offseason. He saw a few different doctors just to research what was going on with his knee and why he didn’t feel as good as he hoped. They all said surgery wasn’t needed, to strengthen everything and he would be fine,” Ainge told 98.5 The Sports Hub’s Toucher and Rich. “We don’t want to rush it.”

Rushing it may have been part of the problem in August, according to Ainge.

“This next year will tell us a lot more. He saw some specialists over the last 6-8 weeks and they all came to the same conclusion, and that gave Kemba a great peace of mind,” Ainge said Tuesday morning as part of his media availability with Boston reporters. “He is on a program and seems to be in a very happy spot. Maybe we didn’t do him justice bringing him back too soon in the bubble.

“We don’t want to make that mistake — if it even was a mistake — this time. It’s not a perfect science, just guess-work and we’re trying to do the best we can to get him as strong and healthy as he can be so he can make it through the year,” Ainge added.

Celtics head coach Brad Stevens said the quick turnaround from the end of last season to the start of the new season are the biggest factor in Walker missing time.

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“I think this has as much to do with the turnaround as anything else. If we were starting games in the middle of January I think he’d be starting right along us and we wouldn’t be talking about this,” Stevens said Tuesday.

While they haven’t had any talks about Walker’s workload when he does return, Stevens does anticipate another “ramping up” period for the point guard.

“He’ll certainly be on a restriction of some kind, and we’ll make sure that, again, we manage as well as we can all the way up to late in the season and if we’re lucky enough to play in the playoffs, hopefully he’ll be peaking at that time,” said the head coach.

Walker played in 56 games in his first season with the Celtics, but was on a minutes restriction with knee soreness when bubble play began in Orlando. He struggled during Boston’s run to the Eastern Conference Finals, especially during the East Semis against the Toronto Raptors, but averaged 19.7 points per game in the Eastern Finals against the Miami Heat.

Walker was one of the most durable players during his eight seasons in Charlotte, missing only 32 games over that span. But he did have knee surgery in back-to-back years in 2015 and 2016 to repair a torn meniscus in his left knee. That has Walker’s durability in question over the next three seasons in Boston.

Boston’s guard depth will be tested early this season, as the team also announced that guard Romeo Langford underwent successful surgery on September 22nd to repair a torn scapholunate ligament in his right wrist. He’s still on pace for his four-to-five month recover, but will also miss the start of the season.

Marcus Smart or Jeff Teague are in line to start games at point guard to start the season, with Tremont Waters and Payton Pritchard also likely set to get some playing time to start the season.

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Stevens said he’ll have a better grasp at how the Celtics will fill the Walker void when the team begins practicing later this week.