Frattin is the team's second-leading scorer, with seven goals and three assists in 10 games this season.
"He had an issue with his (medial collateral ligament) that was corrected (in June), it is something that has flared up and it is not something that the doctors feel is a long-term thing, but definitely have some concern," Coach Randy Carlisle told The Toronto Star.
He indicated Frattin could return to the lineup before March.
The news came shortly it was revealed starting goalie James Reimer will be out of the lineup for at least a week while dealing with an MCL sprain in his left knee.
Goaltender Jussi Rynnas was recalled from the Toronto Marlies of the American Hockey League to fill Reimer's spot.
Rynnas is 8-8-1with three shutouts and has allowed an average of 2.57 goals per game in 17 games this season.