Hawks F Smith sidelined for Game 3 against Celtics
Smith was hurt in Atlanta's 87-80 loss in Game 2 on Tuesday night and tried to work out before Friday night's game, but decided he was unable to play.
Hawks coach Larry Drew said Marvin Williams would start in place of Smith, who averaged 19 points and 15 rebounds in the first two games of the series.
Atlanta is already missing centers Al Horford and Zaza Pachulia.
The series is tied 1-1 with the next two games in Boston. Game 4 is Sunday night.