Lupul was placed on Toronto's injured reserve on Thursday after being injured in the Leafs 4-3 shootout win over the Boston Bruins on Wednesday.
The injury occurred in the second period of the game. Lupul has nine goals and eight assists in 26 games this season.
Toronto forwards Peter Holland and Nazem Kadri will miss over a week.
Holland has been listed as week-to-week by the Leafs after suffering an upper-body injury against Boston while Kadri is expected to miss seven to 10 days.
Kadri missed Toronto's 3-1 loss to Minnesota on Friday night with what the team called a lower-body injury.
In 38 games this year, Holland has eight goals and eight assists while Kadri has 11 goals and 13 assists.