Mats Sundin. (AP Photo/Don Heupel)
Leafs general manager John Ferguson says Sundin suffered the injury in Monday's win over Philadelphia.
The star Swede has eight goals and 11 assists in 17 games this season.
It's the second straight year Sundin has suffered an injury early in the season.
Last year he missed 12 games after he suffered a fractured lower orbital bone when his left eye was struck by a puck in the season opener.