Winger Kirill Marchenko exited against the Calgary Flames in the second period after appearing to suffer an injury.
The injury happened early in the second period after Marchenko got tangled up with Flames forward Yegor Sharangovich and took an awkward fall. He appeared to be favouring his knee as he skated to the bench.
The Maple Leafs announced at the start of the third period that Marchenko had a lower-body injury and would not return.
Marchenko, 26, was acquired by the Maple Leafs on the eve of the season from the Columbus Blue Jackets in exchange for Matthew Knies.
He’s producing at a point-per-game clip with his new team, registering 14 points (six goals, eight assists) in 13 games leading up to Monday.
Marchenko had one shot on goal in 7:05 of ice time prior to his exit.