Bradford Bulls have said that Lesley Vainikolo will leave the club at the end of June to take up a contract with rugby union side Gloucester.
Vainikolo could still be involved in Bradford's Challenge Cup run
The Tongan, 28, is under contract to the Bulls until the end of the 2009 season but asked for a release in order to try his hand at the 15-man game.
The winger has scored 143 tries in his 146 appearances to date with the Bulls.
Bradford agreed to release him after completing the signing of Brisbane Broncos winger Tame Tupou.
Vainikolo could line up alongside Tupou against Harlequins at Odsal on Sunday week and, because Bradford will retain his registration, could return to play for them in the Cup semi-finals and final if they get that far.
We genuinely wish Lesley every success with this move
Bradford chairman Peter Hood
He was officially unveiled as a Gloucester player on Wednesday, signing a three-year deal to join former Bradford team-mate Karl Pryce.
"I want to take this opportunity to thank everyone connected with Bradford Bulls for making the last five years so memorable," said Vainikolo, who joined the club from the Canberra Raiders in 2002.
"Bradford is my home and I know I'll be back. I'm determined to go out on a high and want to contribute as much as possible over the next six weeks before I make the switch."
Bradford chairman Peter Hood added: "Lesley came to see me and said that he still had a burning desire to see if he could replicate his success in rugby league in union.
"There aren't many players who have achieved as much as Lesley has with Bradford or who have given fans so much pleasure with their performances, which I'm not sure we will ever see beaten in Super League.
"In view of this and his five years of unflinching commitment and service to the Bulls, we agreed that, should we be able to secure a world-class replacement, we would not stand in the way of his dream.
"Lesley knows he is welcome back at Bradford at any time and we genuinely wish him every success with this move."