Stevens said it is not likely to be a long-term issue.
Walker had already been ruled out for Friday night’s game against the Timberwolves in Minnesota.
In his first season with the Celtics, Walker is averaging 21.8 points and 5.0 rebounds per game.
In the Celtics’ final game before the All-Star break, he played 46 minutes in a double-overtime win over the LA Clippers. He played 29 minutes on Team LeBron in the All-Star Game.