Henry Speight said the opportunity to make a move to France was too good to refuse and thanked the Reds for allowing it to happen.
After a three-month suspension due to coronavirus, Super Rugby will return in Australia from July 3, albeit in a revamped format.
Izack Rodda, Isaac Lucas and Harry Hockings were released from their RA and Reds contracts on Saturday.
Super Rugby side the Reds have stood down three players amid a pay dispute.
After weeks of talks, professional players in Australia have agreed a deal over an average 60 per cent pay cut.
While there is still no agreement, talks over restructured salaries for players made "good progress" on Sunday, says Rugby Australia.
A new domestic competition will not take place until May at the earliest, with a huge section of the Rugby Australia workforce stood down.
Rugby Australia has invited Western Force to join the Rebels, Waratahs, Reds and Brumbies in a new competition.
The Reds came from behind to beat the Bulls 41-17 and there were Super Rugby wins for the Blues and the Crusaders.
Wollongong set the stage for back-to-back Super Rugby clashes on Friday, with the Brumbies and the Chiefs enjoying victories.