BOSTON (CBS) — The Boston Celtics will be down a big man the rest of the way.

Celtics rookie center Daniel Theis has a torn meniscus in his left knee and will undergo season-ending surgery, according to Yahoo Sports’ Sham Charania.

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The injury, which Theis suffered during Sunday night’s 99-97 loss to the Indiana Pacers in Boston, will end an impressive rookie campaign for the 25-year-old German. Theis averaged 5.3 points and 4.3 rebounds off the Boston bench, providing the C’s second unit with rebounding, defense and some rim protection, along with a little bit of a shooting touch from the outside. He was seen as one of the NBA’s best bargains this season after Danny Ainge signed him to the league minimum over the offseason.

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Boston is losing one of their best bigs off the bench and will now have to rely more on centers Aron Baynes and Greg Monroe. They could ask rookie Semi Ojeleye to take on an expanded role in Brad Stevens’ rotation in Theis’ absence.

The Celtics are dealing with a handful of injuries with just 15 games left in the regular season, though Theis is the only one lost for the season. All-Star guard Kyrie Irving may miss some extended time with knee soreness and guard Jaylen Brown isn’t expected to play this week after suffering a concussion last Thursday, while Marcus Smart (thumb) and Al Horford (illness) are dealing with minor issues.

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The Celtics have Monday and Tuesday off before hosting the Washington Wizards on Wednesday night.