After the 4-3 overtime loss, Mike Babcock said Muzzin suffered a charley horse, according to TSN's Mark Masters. The head coach didn't provide a potential recovery timeline.
Muzzin took a hard hit against the boards from Tom Wilson and left the game in discomfort.
The Maple Leafs were forced to finish the game with five defensemen. But luckily for them, blue-liner Travis Dermott returned to the lineup for his season debut on Tuesday after a 13-game absence.
Muzzin has played a massive role on Toronto's back end to start the season. He's notched nine points while averaging over 23 minutes per night, which ranks second among all Maple Leafs skaters.