Hayward left the game in the second quarter after making contact with LaMarcus Aldridge during a pick. He headed straight to the locker room.
The Celtics said an X-ray exam confirmed the diagnosis and that Hayward was ruled out for the game.
Hayward was averaging 20.3 points per game during Boston’s 6-1 start to the season.
Two years ago, he missed the entire season after suffering leg and ankle injuries six minutes into the Celtics’ season opener.