Miro Heiskanen is considered month to month for the Dallas Stars after having knee surgery Tuesday.
The defenseman left a 4-3 overtime win against the Vegas Golden Knights on Jan. 28 at 7:56 of the third period after Vegas forward Mark Stone collided with his left leg.
Stars coach Pete DeBoer said Heiskanen had an MRI on Jan. 29.
Heiskanen already had been ruled out for Team Finland for the 4 Nations Face-Off, which will be held Feb. 12-20 in Montreal and Boston. He had been selected for the team, along with Dallas teammates forward Roope Hintz and defenseman Esa Lindell.
With injuries to Heiskanen and defenseman Jani Hakanpaa of the Toronto Maple Leafs, Urho Vaakanainen (New York Rangers) and Henri Jokiharju (Buffalo Sabres) were named as replacements for the best-on-best tournament.
Heiskanen has 25 points (five goals, 20 assists) and leads Dallas with an average ice time of 25:10 in 50 games this season.
"With Miro, he's not a guy that you can replace with one guy," forward Wyatt Johnston said Thursday. "It's a matter of everyone stepping up to fill that void, which obviously isn't easy. We have a lot of great hockey players here. It requires everyone to step up and do what they can to help the team."
The Stars (34-18-1) had a five-game winning streak end Tuesday with a 2-1 loss at the Anaheim Ducks. They are second in the Central Division, 10 points behind the Winnipeg Jets.
"You lose the best defenseman in the NHL, everyone has to step up," goalie Jake Oettinger said. "That starts with me. We've done that all year. We've lost big pieces all year and we've rallied around it and stepped up. I can be a huge part of that. I'm focused on playing my best hockey right now until the [4 Nations Face-Off] break and trying to step up big while Miro is out. Hopefully I can do that."
NHL.com independent correspondent Taylor Baird contributed to this report