Rielly was hurt in a collision with New York forward Kyle Palmieri early in the third period of Toronto's 3-2 overtime loss to the Islanders at home Monday night.
Rielly has no goals and 16 assists in 20 games this season and is averaging 23 minutes of ice time.
The decision gave Toronto some salary-cap flexibility to promote reinforcements from its American Hockey League affiliate. As such, the Maple Leafs were able to recall defensemen Mac Hollowell and Victor Mete.
Maple Leafs coach Sheldon Keefe said following practice Tuesday that the 28-year-old Rielly doesn't need surgery, adding there's no firm timeline for his return beyond the minimum 24 days and 10 games required for going on long-term injured reserve.
The Associated Press contributed to this report.