The Boston Celtics on Sunday afternoon pulled off an impressive comeback win in Game 3 against the Cleveland Cavaliers by completely erasing a 21-point deficit.

However, when the Celtics take the floor on Tuesday night for Game 4, they will likely do it without the services of veteran center Amir Johnson due to a shoulder injury, according to Gary Washburn of the Boston Globe.

The Celtics could be without center Amir Johnson in Game 4 of the Eastern Conference finals Tuesday, as he sprained the AC joint in his right shoulder in Game 3, an injury that prevented him from shooting the ball.

The injury occurred in the first quarter after he got tangled up with Cavaliers big man Tristan Thompson while battling for a rebound. He exited the game shortly after heading to the locker room but did re-enter in the second quarter wearing a compression shirt to help protect his shoulder.

Johnson did not take any encouraging steps forward on Monday as he did not participate in practice and is scheduled to undergo an MRI on his ailing shoulder. The 30-year-old has played in a limited role in the playoffs averaging just 2.7 points, 2.1 rebounds, and 0.5 blocks in 10.7 minutes per game.

His potential absence would leave the Celtics without a defensive big man that could help clog the paint against the Cavaliers in a critical Game 4. Head coach Brad Stevens may turn to a smaller starting lineup that features Gerald Green, who has started seven games in this year's playoffs.