PITTSBURGH -- Ottawa Senators defenseman Erik Karlsson will need surgery to repair his left Achilles after the tendon was cut by a skate blade late in the second period Wednesday night against Pittsburgh.
The Norris Trophy winner last season as the NHL's top defenseman, Karlsson was cut by Penguins forward Matt Cooke's skate blade as the two tangled along the boards.
Karlsson leads NHL defensemen with six goals, scoring three times in his previous four games. He had a short-handed goal to help the Senators beat Buffalo 2-0 on Tuesday night.
"It's a tough blow," Senators captain Daniel Alfredsson said. "Obviously, the way he's playing, and how much he means to our team, it feels terrible and I feel really bad for him."
Karlsson immediately fell to the ice and was in visible pain. He needed help getting back to the bench and showed frustration, throwing his stick against the boards before disappearing down the runway.
"You knew right away there was an issue," Senators goalie Craig Anderson said. "He's a player who is irreplaceable. It's unfortunate, but there are no words that can explain what we're feeling."
Cooke has been suspended several times for hits, some of them involving head shots that injured opposing players. In 2011, Cooke was suspended for the Penguins' final 10 regular-season games and the first round of the Stanley Cup playoffs after jabbing an elbow to the head of New York Rangers defenseman Ryan McDonagh.
"We all know who's involved in it," Senators coach Paul MacLean said. "That's just the way it is. The injury to Erik was unfortunate, and it happens on a nothing play that could've potentially been whistled down."
The NHL, however, said there will be no hearing or any supplemental discipline for Cooke in the wake of Karlsson's injury.
"I feel horrible for Erik Karlsson, I feel bad for Ottawa," Penguins general manager Ray Shero told ESPN.com Thursday. "It's a bad feeling. But I can't rationalize where that was a dirty play or anything with intent. Our fan base knows how it feels to lose a star player. It's emotional. I know how it feels like. It's just very unfortunate. I would not be defending Matt Cooke if I thought it was a dirty hockey play."
The NHL's department of player safety reviewed the incident and NHL disciplinarian Brendan Shanahan spoke with general managers for both the Senators and Penguins, but there is nothing coming Cooke's way. The league doesn't view the play as illegal or malicious.
Information from ESPN.com's Pierre LeBrun and The Associated Press was used in this report.