by Jeff Zillgitt, USA TODAY Sports

Boston Celtics rookie forward Jared Sullinger underwent back surgery Friday and will miss the rest of the season, the team announced.

Sullinger, whose back had been bothering him the past two weeks, appeared in 45 games, averaging six points and 5.9 rebounds in 19.8 minutes per game.

NBA doctors issued a medical red flag on Sullinger’s back just before the draft, causing the potential lottery pick to fall to No. 21 in the June draft. The Celtics were aware of Sullinger’s back and had no reservations selecting him, considering him a steal at that point in the draft.

Celtics President of Basketball Operations Danny Ainge defended the decision to draft Sullinger.

“The way I look at it there’s risk in every player for one reason or another,” Ainge told USA TODAY Sports in October. “There’s very few players who are no risk. There’s all kind of different risks. One risk is, are they good enough. One risk, are they healthy health enough. Another risk is do they have character. Another risk is do they fit in with our system and with our personality. So you’re always risking something with most players.

“Jared has had a bad back, and there is risk there. We’re well aware of it, and we’re doing all we can to help Jared and help his body and help him reach his full potential. So far, he’s been good.”

It is another tough injury for the Celtics, who lost point guard Rajon Rondo for the season when it was discovered on Sunday that he had a torn ACL in his right knee.

Contributing: Sam Amick

… [For more on Celtics' Jared Sullinger has back surgery, done for the year, click here.]