It's unclear when Tavares was injured. He skated 17:14 and had one shot on goal in a pre-season game against the Senators on Saturday.
The Maple Leafs are dealing with a list of injuries just one week into training camp, with Pierre Engvall (foot), Adam Gaudette (shoulder), Timothy Liljegren (hernia) and Jake Muzzin (back) all missing some time early on.
Tavares, 32, is coming off a bounce-back season in which he scored 27 goals and 76 points.
The Maple Leafs resume their pre-season schedule Wednesday night against the Montreal Canadiens. Puck drop on Sportsnet ONE and SN NOW is at 7 p.m.