The 29-year-old Lupul was in front of the net during a power play midway through the second period when a slapshot from teammate Dion Phaneuf smashed into his arm. Lupul left the game immediately and did not return.
Lupul signed a five-year contract extension with the Maple Leafs on Sunday. He led Toronto with 25 goals and 42 assists last season and made his first All-Star team. Lupul had yet to score for the Maple Leafs this season at the time of the injury.