The forward left a 3-1 loss to the Oilers in the third period Wednesday after he was hit along the boards by Edmonton forward Josh Archibald 2:51 into the period. Thornton appeared to be favoring his left arm as he skated to the bench.
"No update other than he won't be available tomorrow," Maple Leafs coach Sheldon Keefe said Thursday. "And as I said last night, it looks like he's going to miss some time. It's not a day-to-day thing at this point, but we don't have a final update or diagnosis at this stage."
After briefly sitting on the bench, Thornton went to the dressing room and did not return. He played 13:12 and had one shot on goal.
The 41-year-old signed a one-year contract with the Maple Leafs on Oct. 16 after playing 15 seasons for the San Jose Sharks. He has two points (one goal, one assist) in five games this season playing primarily on a line with Auston Matthews and Mitchell Marner.
Matthews skated briefly Thursday before leaving the ice. Keefe said the center wasn't feeling well after the game Wednesday.
"No update," Keefe said. "He's just going to take the rest of the day here today and see how he is tomorrow. I'll update in the morning."
NHL.com staff writer Mike Zeisberger contributed to this report
