Franson was shoved from behind by Sabres forward Torrey Mitchell behind the Toronto net at 11:15 of the third.
Franson had to be helped off the ice and did not return.
The Leafs also announced that forward David Booth suffered a lower body injury and would not return.
Buffalo lost a pair of bodies in the first.
Patrick Kaleta took a Morgan Rielly slap shot to the face at 11:32 of the opening period.
Sabres Johan Larsson skated into the elbow of an unsuspecting Petter Granberg and headed for the dressing room with a minute left in the first.
Neither Buffalo player returned.