Stars GM Jim Nill speaks to the media about Mattias Janmark's knee surgery here.

Stars winger Mattias Janmark had knee surgery Friday and will be out a minimum of five to six months, general manager Jim Nill said.

Janmark, 23, was discovered to have Osteochondritis dissecans, a joint disorder in which cracks form in the cartilage and bone, causing blood deprivation and making the knee lock up.

Nill said the condition is genetic and added that chances of full recovery are not 100 percent. He expects to know more when he talks with doctors over the weekend.

"I was told 80 percent chance of full recovery," Nill said. "We'll go from there."

Janmark had been skating in camp and was expected to play in the Stars' preseason game Wednesday in Colorado when his knee locked up.

"What happened with Mattias is he had a small segment, approximately 21 millimeters by 11 millimeters, that became displaced and is locked in his knee," Nill said, adding that doctors planned to take the bone segment and reattach it to the area from where it came.

"It's the bone and the cartilage, they both came off together," Nill said.

Nill said Janmark might still play this season.

"Healing and rehabilitation is approximately five to six months," Nill said. "Possible return in April, we're looking at maybe being available during the playoffs. We'll have to play that by ear."

Janmark had a great rookie season in 2015-16. Acquired from Detroit near the end of the 2014-15 season as part of the Erik Cole trade, Janmark surprisingly made the team out of camp and played in 73 games. He tallied 15 goals and 14 assists while averaging 14:10 in ice time per game. He played much of the time on a line with Jason Spezza and was expected to return to that line this season.

The Stars already have lost Cody Eakin for six weeks with a knee injury. Eakin is expected back in early November. In addition, Tyler Seguin (heel), Devin Shore (ankle) and Ales Hemsky (groin) aren't available for play as they are rehabbing injuries. Nill said he expects Seguin, Shore and Hemsky to be ready for the start of the regular season Oct. 13.

"Tyler is feeling better, hoping maybe start skating next week," Nill said. "Still on schedule to be available for start of season. Devin Shore, we think he'll be skating full-time on Monday."

Still, losing Janmark is big. He is a strong two-way forward who can also fill in at center during times of injury.

"It's obviously a big loss," coach Lindy Ruff said. "He played a lot of different positions and a lot different situations. I think he was a real important piece for us."

Nill said he does not believe the team needs to seek an additional forward at this time.

"We're very comfortable with what we have," he said. "This is part of the game. We've got lots of depth, and this is an opportunity for somebody else."

Of the 14 forwards originally expected to battle for a spot on the opening day roster, the Stars have lost Janmark and Valeri Nichushkin (signed in Russia). That opens the door for players such as veterans Adam Cracknell and Travis Morin, as well as prospects Brendan Ranford, Cole Ully, Remi Elie and Gemel Smith.

"It's definitely an opportunity for guys who maybe wouldn't have gotten as strong a look," Ruff said. "That enthusiasm for those players should be pretty great right now. Players realize numbers, they realize opportunities."

Twitter: @MikeHeika