Nagas has failed to take the field this season for the Raiders after undergoing an operation in the NRL off-season which he hoped would extend his career.
The operation - which involved the injection of a silicone-like substance into the knee joint - allowed the 29-year-old to resume training, however, he was unable to stretch out.
"I have enjoyed the highest honours in a game I loved and couldn't wish for any more," Nagas said today.
"I am just disappointed that I couldn't get a few more games out of my old knee, but that's just the way it is."
Nagas, who will remain with the club in a junior development role, played 142 first grade games for the Raiders, winning a premiership in 1994.