The 31-year-old joined from the Sydney Roosters and scored 25 tries in 49 appearances for the Stobart Super League club.

Roberts was in blistering form early in 2010 before rupturing his posterior cruciate knee ligament in a 54-14 win over Wakefield after colliding with the post.

The Australian's four-year deal was due to expire at the end of the season and he has now conceded defeat in his bid to return to full fitness.

"On behalf of myself and my family, a big thanks to all the fans and staff," Roberts wrote on his Twitter account.

"Much love and respect, we've enjoyed our time here."