Drouin, a forward, did not play in a 5-1 loss to the New Jersey Devils on Tuesday. The Canadiens made the announcement following the game and said Drouin sustained the injury Nov. 5 during a 6-4 loss to the Vegas Golden Knights.
He has four assists in 12 games this season.
Drouin and Canadiens forward Joel Armia each had a maintenance day Monday and did not practice after they were able to play in Montreal's 5-4 overtime win against the Pittsburgh Penguins on Saturday.
Armia was not with the Canadiens when they lost 6-4 at the Columbus Blue Jackets on Thursday. He has no points in seven games and missed Montreal's first eight games this season because of an upper-body injury.
"I don't know how severe it is," St. Louis said Wednesday. "He just needs a little more time."
