David Gallop has called for help from the International Rugby Board to quash Sonny Bill Williams' apparent bid to play rugby union in France, a move which would end his NRL career for good.

"If Sonny Bill were to play overseas, the door would be closed on him returning to the NRL at anytime in the future," Gallop declared.

The NRL chief executive's stunning call for co-operation from a code which was subject to almost 100 years of rugby league raids on its player ranks comes as some legal advice suggested any attempt at an injunction to prevent Williams breaking his Bulldogs contract may not work.

Bulldogs teammates led by skipper Andrew Ryan expressed shock and dismay at Williams' unannounced walkout, while fans and officials voiced outrage.

The Kiwi international was believed to have flown to France on Saturday night to join cashed-up Toulon on a deal worth $3 million over two seasons, despite the newly-promoted French first division club denying signing him.

William's sensational exit had the NRL community reeling, coming less than a week after fellow superstar Mark Gasnier announced he would join former Kangaroo Craig Gower in the French rugby ranks.

Gallop said the Bulldogs would have the NRL's full support in their fight to ensure Williams honoured the remaining four years of the five-season, $2.5 million contract he signed in March last year.

"We'll also be calling on the IRB to step in and get involved. This can't be good for either of the codes," Gallop said.

"Contractual stability is important to both and, if they don't get involved, then they're condoning a form of international piracy."

Gallop said Williams' actions seemed out of character for a player who'd been keen to promote himself as a role model for youngsters and fellow Polynesian players.

"He's obviously troubled," Gallop said. "You don't just walk out without notice unless you're very troubled, in my view."

In another twist, Khoder Nasser - the man some were blaming for Williams' departure - denied he was the 22-year-old's manager despite having assisted him in recent months.

"I would like to make this point strongly. I am not authorised at any stage to speak on behalf of Sonny Bill Williams," Nasser said from Newcastle where he was promoting client Anthony Mundine's Wednesday fight.

The controversial agent also indicated there was more to the saga than met the eye.

"As a friend, I mean, what is done is done and we won't know until we hear from him," Nasser told Channel Nine.

"There's a lot of things running through his mind and he must have obviously thought that was the best thing to do at the time."

Bulldogs boss Todd Greenberg said the issue was one not just for rugby league but Australian sport as a whole to deal with.

"It has some big ramifications and we need to get the buy in of a whole range of codes," Greenberg said.

"This is not good for anyone in any sport that someone can take a contract, sign it and then go and find somewhere else to go.

"We need to work hard together in unison to make sure that happens.

"It's a test case for Australian sport too that the sanctity of a contract in this country needs to remain exactly that.

"We need to stand up here. We need to stand up not just as a club but as a game.

"It's not about trying to change Sonny's mind ... it's about standing up for the right of the contract."

Greenberg admitted he would listen to offers of compensation from Toulon or any other potential suitors - but stressed he knew nothing of Williams' plans.

Gallop refused to join those blaming Nasser for Williams' walkout.

"These are young men but they are adults and they've got to make their own decisions," he said.

"Life is about making choices, no matter what your advice is from your agent or anyone else.

"Sonny Bill Williams made this decision to walk off without notice ... it goes way beyond contracts and money - what we're talking about here is someone walking out on their teammates mid-season.

"It flies in the face of everything that kids are taught."

Bulldogs skipper Ryan said Williams' mid-season walkout was "very hard to swallow when we've been busting our butts at training and in games every week".

Williams' former teammate Willie Mason refused to comment on the drama, but Roosters skipper Craig Fitzgibbon admitted his defection would be a major blow.

While most were condemning Williams, Fitzgibbon was prepared to give him the benefit of the doubt.

"There must be a horrible reason behind the scenes as to why he's so dirty on Canterbury. I'm not sure what it is," Fitzgibbon said.

"I guess we have to move on ... if he doesn't want to be here, there's no point hanging on to him.

"In saying that, I can't recall a player as talented or as awesome to watch as him in long time.

"We're going to miss him."

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