Tony Allen scored 19 points for Boston before leaving with an injured left knee with 3:01 remaining in the third quarter.

Allen went up for a free dunk and landed awkwardly, writhing in pain for several minutes until his teammates carried him off the court.

Allen was taken to New England Baptist Hospital for an MRI.

"This is just terrible," Celtics coach Doc Rivers said. "When he came down, you could see his heel jam into the ground and I reacted right away because I could see it, I could feel it"