Boston Celtics center Daniel Theis underwent arthroscopic surgery on his left knee to have a loose body removed, the team announced.

While the Celtics didn’t release a specific timeframe for his return, Theis is expected to be available for the upcoming season, not expected to start until late December at the earliest.

Theis, 28, averaged 9.2 points and 6.6 rebounds in 65 regular-season games.

He had surgery on the same knee in March 2018 to have his lateral meniscus repaired.