Ottawa Senators defenseman Erik Karlsson suffered a cut to his left Achilles tendon during Wednesday's game against the Pittsburgh Penguins.
Late in the second period, Karlsson and Pittsburgh's Matt Cooke met along the boards while chasing down a puck, and Cooke's left skate appeared to graze Karlsson near the left ankle.
Karlsson had to be helped off the ice as he was unable to put any pressure on his left leg.
"I feel terrible," said Cooke. "I'm not trying to do that, obviously. It's happened a few times over the past few years. It's scary. I was trying to hit him. Not like that."
Between periods the Senators announced that Karlsson had a cut to his lower leg, but later revealed on the team's Twitter page that he suffered the laceration and will have to have surgery.
The reigning Norris Trophy winner will be out indefinitely.
"The injury is unfortunate that it happened on a nothing play," said Ottawa head coach Paul MacLean. "It could have been potentially whistled down and we all know who was involved in it and that's just the way it is. Injuries are a part of the game. We're going to have it re-evaluated when we get back to Ottawa."
Karlsson has six goals and 10 points over 14 games this season.