Just two years ago promising young Penrith Panther Adam Docker was being touted as a future Kangaroo.

But after just four seasons in the NRL, the 24-year-old forward has been forced to retire because of injury.

After fighting back from multiple concussions, Docker has decided to call it quits because of severe pain in his left knee which has no cartilage.

“It’s the highest grade arthritis you can get,” Docker told foxsports.com.au. “It’s even chipping away at my bone.

“I’ve been to three different surgeons and a stem cell surgeon and some outside of my club to get different opinions.

“They all pretty much said the exact same thing that I shouldn’t be playing on it and there’s nothing I can do unless I get a knee replacement and I’m too young for that.”

After signing for the Panthers, Docker made the NSW Emerging Origin squad and was a part of the Kangaroos train-on squad.

“From start to finish, I am totally happy with what I’ve done,” he said. “My childhood dream was to play first grade and I did.

“As much as footy was a huge part of my life, life’s got to go on,” he said.