Kings’ Jeff Carter is out indefinitely following surgery for a cut on his leg; Brooks Laich is signed as replacement

What appeared to be an incidental hockey play will end up costing the Kings one of their major offensive pieces.

Jeff Carter underwent surgery for a cut on his leg Thursday and is out indefinitely, general manager Rob Blake announced. Carter injured his ankle tendon when was struck by the skate blade of Montreal Canadiens defenseman Jeff Petry on Wednesday as the two met at the boards with glancing contact.

“It was just a harmless play,” Kings coach John Stevens said. “I was hoping at that time that it was just a shot-blocker [guard] or something that came loose, but obviously it wasn’t the case. It’s a fast game with steel blades on your feet, so things can happen in a hurry.”

Carter led the Kings with 32 goals last year and gives them a premier top-two center combination with Anze Kopitar. He formed an effective line with Tyler Toffoli and Tanner Pearson and plays in all situations.

The Kings were not considered deep at the position beyond Kopitar and Carter, so the injury further challenges them. But it opened the door for veteran Brooks Laich. The Kings signed him Thursday to a one-year contract worth an announced $650,000.

In a seemingly unprecedented move, Laich, 34, has practiced as an unsigned non-roster player since his initial tryout contract expired — a situation Laich said he was prepared to do until at least Christmas. It was a beneficial agreement for both sides, and Laich was happy it worked out, albeit by unfortunate circumstance.

“That does happen in the game,” Laich said. “That’s a tough bounce for Jeff. Myself, that’s why I was able to be patient. That’s why I stuck around, came to practice, just because anything is possible in the game of hockey. … I’m grateful that they allowed me to stick around in practice. Sometimes you get a little bit of luck and you get an opportunity down here to make the most of it.”

Laich centered a line Thursday with Justin Auger and Andy Andreoff, while Nick Shore took Carter’s spot with Pearson and Toffoli. The Kings already endured an injury to Alec Martinez, and Stevens expected them to adjust without Carter.

“He’s a huge part of our team,” Stevens said. “But it’s next-man up now. We’re going to have guys with increased responsibilities. We’re going to have guys playing with different people. I think we’ve seen before when guys get opportunities, sometimes guys are excited to take advantage of those opportunities.”

In another move Thursday, the Kings signed defenseman Derek Forbort to a two-year contract extension worth $2.52 million annually. The deal spoke to Forbort’s development through their system and into a partnership with Drew Doughty the last two seasons.

“He took a huge step last year,” Stevens said. “He had a great camp and came in and really proved that he belonged in the league. He’s really formed an identity as a player that we like on our hockey team.”

curtis.zupke@latimes.com

Twitter: @curtiszupke