Sonny Bill Williams will return to Japan today with his Sydney Roosters contract yet to be registered by the NRL.

Despite lodging a $550,000 one-year ''vanilla'' contract with the NRL on November 19, Roosters officials are still waiting for the salary cap auditor Ian Schubert to approve the deal.

With Channel Nine choosing the Roosters to kick off the season against South Sydney on March 7, and the Warriors moving their round two clash with the Bondi-based club to Eden Park to capitalise on Williams' drawing power, it is hard to imagine Schubert blocking the All Blacks star's return to the NRL.

But after Israel Folau's bid to join Parramatta failed to materialise due to his frustration over the protracted negotiations, no one at the Roosters is taking anything for granted.

''It is in the hands of the NRL,'' Roosters chief executive Brian Canavan said. ''There is obviously a bit more correspondence to go back and forth but it has been lodged with the NRL, and we're just waiting now.''

Williams, who had a brace on his right arm removed last Wednesday, will continue rehabilitation from pectoral muscle surgery with Japan's Panasonic Wild Knights.

However, he is unlikely to play again for the Top League rugby union club this season, and will begin boxing training in early January for the World Boxing Association international title fight against South Africa's Francois Botha on February 8.

''I have got 10 weeks, four weeks of which will be physio and getting the injury ready and then hopefully six weeks preparation for the fight,'' Williams said.

''We are looking to having camp in Japan and bringing over a trainer and a couple of sparring partners, along with Quade [Cooper] also, which will be pretty cool.''

Cooper will make his boxing debut on the undercard of the Williams-Botha bout.

The New Zealand heavyweight champion then plans to return to Sydney to begin pre-season preparations with the Roosters.

''I have spoken to a lot of specialists, and the thing all the specialists have said is that I will be ready for boxing before coming back to the rugby field just because of the uncontrolled situations you get in on the rugby field,'' Williams said.

''Normally I guess it is a big risk, but it is a risk I have to take because I don't want to be out of the boxing ring for a year and a half. It is not good.

''Obviously the fight is for a WBA international title ... It is something I need to do, and I will be training as hard as I can for.''