John, 24, has been on the fringes at the Rapid Solicitors Stadium ever since the arrival of Paul Sykes on loan midway through last season.
It has seen him limited to just 14 appearances since arriving at the club from New Zealand Warriors at the start of 2012.
Head Coach Richard Agar said: “He has got a club in the NRL that he’s going to go and join one of their full-time squads so we’ve agreed to release him with immediate effect.
“For Isaac at 24-years old with no reserve grade or ability to dual-reg him because of the border agency rules the landscape from halfway through last season to where we are now has completely changed. He was part of our squad and we were really happy to be part of our squad but he can’t play, we have nowhere for him to play.
“While these two (Smith and Sykes) are fit and on form and Isaac knows this, it is hard for him to shift them at the moment. That’s the game we’re in at the moment unfortunately so for him he needs to play and he wants to play for his own career and his development.
“We’ve had an understanding that if an opportunity came up for him we wouldn’t stop him from taking it. Good for him that the opportunity has come up and we’re going to wish him all the best and really thank him for his contribution.”
He added: “I am very grateful for the club to allow me to leave, the move didn’t work out as well as I hoped and I’m really looking forward to my new challenge.”