Muzzin collided with Coyotes forward Clayton Keller during the second period of the contest and was slow to get up before eventually skating off the ice. He did not return to the game and a timeline for his return has not been announced.
Maple Leafs star Mitch Marner expressed concern for Muzzin's health after Monday's game, shedding light on how close the two players have become over the past several seasons.
"I've been saying a lot that's probably my best friend on this team," Marner told reporters. "Outside of hockey, this is way bigger. He's got two unbelievable daughters, an unbelievable wife and you just wish the very best for him. You have so much to live for in this life with your family, so hopefully everything's OK with him.
"And we're very blessed to have an unbelievable medical staff here that takes care of their players very well and knows what to do. So I'll try to check in with him here soon. Obviously he's one of my best friends; brothers, really."
The 33-year-old Muzzin has battled a number of injuries in recent years, including a history of concussions. He also missed time during training camp this fall due to a nagging back issue.
Muzzin has one assist in four games so far this season, and has registered 18 goals and 63 assists for the Maple Leafs since he was acquired from the Los Angeles Kings in 2019. The Woodstock, Ont., native is in the middle of a four-year contract that carries a $5.625 million cap hit.
Defenceman Filip Kral was recalled from the AHL's Toronto Marlies to take Muzzin's place on the roster. Kral has been held off the scoresheet in two games for the Marlies this season. He recorded three goals and 18 assists in 58 AHL games in 2021-22.
Toronto returns to action Thursday when it hosts the Dallas Stars.
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