Washington Capitals star Alex Ovechkin left Monday night's 3-2 win at Carolina in the opening period with an apparent right knee injury.
A spokesman for the Capitals said Ovechkin's injury would be evaluated overnight and that any further information from the team would come Tuesday morning.
Ovechkin was injured with 7:55 left in the first period.
He appeared to initiate a knee-to-knee collision with Carolina's Tim Gleason as the defenceman attempted to take the puck out of the Hurricanes' zone.
"Any time Alex is hurt I'm concerned," Washington coach Bruce Boudreau said. "He's stiff right now.
"But I don't know how long he's going to be out if he's going to be out at all. Tomorrow, you know, these things, the next morning you find out a bit more than you do now."
Ovechkin was down on the ice for several minutes before he was helped off, grimacing while he was bent over at the waist. He was given a five-minute major penalty for kneeing and a game misconduct, his second game misconduct penalty in the last three games.
Gleason also was helped to Carolina's dressing room for an injury assessment, but he returned to the ice during the power play that followed Ovechkin's penalty.
"The first thing is I'm hoping and I still hope it's not too bad," Washington goalie Jose Theodore said of Ovechkin.
"It's never fun when you see the best player in the game and your best player down like this. You always worry about something really bad.
"When Alex is out, everybody's got to pick it up. He's a big part of this team, and I thought tonight everybody picked it up."
Ovechkin leads the Capitals with 18 goals, 30 points and 44 penalty minutes.