Evgeni Malkin returned to the Pittsburgh lineup Friday night in Buffalo after missing five games, but it could be his last game action in a long while.
Malkin, 24, has been bothered by knee issues this season. He was hurt again during the first shift of the second period after a collision with Sabres defenceman Tyler Myers.
"Evgeni Malkin had an MRI [Saturday] morning," Penguins coach Dan Bylsma told the team's website. "The results show that he has a torn MCL and ACL. At this point in time we are discussing options with the doctors on what to do next.
"This is a difficult injury for him. It was kind of a fluke situation going into the boards with a guy. That's a tough injury for Geno. We have dealt with games without him. We've managed to find our way without him. That's what we're going to have to look at now.
"We're discussing options with our doctor. Surgery is a possibility. I'm not sure if there is a rehab possibility. But right now I just got the news on the MRI."
Malkin had 15 goals and 22 assists in 43 games this season and was held without a point as Pittsburgh blew a two-goal lead in a 3-2 loss to the Sabres.
The Penguins face the Washington Capitals on Sunday afternoon, the first meeting between the clubs since the Winter Classic on New Year's Day.
Pittsburgh is already without star Sidney Crosby, who hasn't played since Jan. 5 due to concussion symptoms. Crosby suffered a hit to the head in the Winter Classic game as well as the team's next outing, against Tampa Bay.
The Penguins learned earlier this week that surprise story Mark Letestu, in his first year with the club, will miss at least four weeks after arthroscopic knee surgery.