Ottawa Senators coach Paul MacLean says his team will need to change their style of play and grind out more wins to contend for a playoff spot after losing star defenceman Erik Karlsson for the season.

The 22-year-old Karlsson will be out at least three to four months after he suffered a 70 per cent laceration of his Achilles' tendon.

He had what MacLean called a succesful surgery Thursday at The Ottawa Hospital.

Karlsson, who won the Norris Trophy last year as the NHL's best defenceman, is arguably the Senators most dynamic offensive player. He had scored six goals and four assists in 14 games this season.

The Senators are also without centre Jason Spezza, who is out for the season after back surgery.

Karlsson could 'make something out of nothing'

MacLean told Robyn Bresnhan on Ottawa Morning Friday the Senators still plan to play "fast" but said relying on five or six goals a game to win may not be realistic.

"I think that any team that loses their top two offensive catalysts in Jason Spezza and Erik Karlsson is certainly going to be a different team because you don't have those special players that can just make something out of nothing happen on the ice," said MacLean.

"But I think our identity as a team is not going to change. We've always been a work-ethic-based hockey team and one thing that will have to happen is we'll have to play with a little bit more structure," he said.

MacLean said Karlsson's injury will be an opportunity for some of the team's young defencemen to step in, but said "we don't have someone like Erik Karlsson to replace Erik Karlsson."

'A reckless play by a reckless player'

Karlsson was injured when Pittsburgh Penguins forward Matt Cooke's skate blade came down on the back of his left leg as the two tangled along the boards. It happened in the second period of Wednesday night's 4-2 loss to Pittsburgh.

Karlsson fell to the ice and was in visible pain after tangling with Cooke. He needed help getting back to the bench and displayed frustration, throwing his stick against the boards before disappearing down the runway.

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 playoffs after an elbow to the head of New York Rangers' defenceman Ryan McDonagh.

MacLean reserved judgement on whether Cooke should have been suspended but called it "a reckless play by a reckless player."

"Any time Matt Cooke is involved there is always going to be questions around the league. That is the reputation he has and that's not just me saying that that's the baggage he brings with him," he said.