MILWAUKEE — Boston Celtics big man Robert Williams won’t play in Game 4 of the Eastern Conference semifinal series against Milwaukee on Monday because of soreness in his surgically repaired left knee.

Williams had surgery to repair torn cartilage in his knee on March 30. The 6-foot-9 forward/center didn’t return until Game 3 of the Celtics’ first-round series with the Brooklyn Nets. He had started each of the first three games against the Bucks.

“It’s not unexpected to have this after a surgery,” Celtics Coach Ime Udoka said before the game. “There’s been soreness at times, but it’s a little more irritated today.”

Udoka said Grant Williams would replace Robert Williams in the Celtics’ lineup Monday. Udoka was optimistic that Robert Williams would be available for Thursday’s Game 5.

Robert Williams has averaged 8.7 points, 5.7 rebounds, 2.7 blocks, 1.7 assists and 23.3 minutes in this series. The Celtics trail the defending champion Bucks 2-1.

Williams took an elbow to the face from Milwaukee’s Bobby Portis during the Bucks’ 103-101 Game 3 victory.