Gallagher left Thursday's loss to the Stars with a lower-body injury early midway through second period but returned for the third period, Pat Hickey of the Montreal Gazette reports.
Gallagher appeared to suffer an injury to the knee or groin area when his left leg buckled along the boards. He skated to the bench under his own power and was assisted to the dressing room by training staff. Upon returning to the ice for the third period, Gallagher took six shifts for 4:03 TOI. The injury bears monitoring Friday ahead of Montreal's next game, Saturday at home against the Senators.