A source close to Williams also said he had an ongoing back complaint and was unhappy with how the club had managed it.

He was also upset with what he perceived as excessive media scrutiny into his private life and, at the urging of the club, having to admit he had problems with alcohol last year.

The shock walk-out is sure to spark a legal stoush. Bulldogs officials are confident there is no get-out clause in his contract.

Williams has four years to run on the $450,000-a-year deal with the Dogs and a lot of the club's marketing revolves around him.

"It just defies logic, it really does," said Bulldogs chief executive Todd Greenberg, who was informed of Williams' departure by Nasser. "For a 22-year-old to pick up and go, it's a big call. It's unacceptable to walk out on a contract - it's unacceptable to your teammates, in particular. As a minimum, all fans deserve an explanation. We've all been let down."

The Bulldogs were last night looking to put an injunction on Williams to prevent him from playing in any rival team or competition.

"We're looking to take out an injunction which will stop him playing for anyone else, any code or any club," Greenberg said. "I'm determined to ensure if he's not playing for the Bulldogs, he's not playing at all. Full stop."

There were early suggestions that Williams could have problems getting registered in France.

The cut-off point to register players is July 14 - the same stumbling block that prevented Mark Gasnier from playing there last season when he wanted to leave St George Illawarra.

Previously there had been rumours he had signed on July 9.

Revelations that the club's biggest drawcard has left have outraged fans and confirmed that French rugby clubs are serious about poaching the best stars in rugby league.

Gasnier and Craig Gower have already signed with French clubs, while Newcastle's Adam MacDougall is set to leave league.

Williams's move is an even bigger slap in the face to the club and supporters considering the lengths Greenberg had gone to to keep his superstar happy. Only last weekend, the Bulldogs opened up the gates for free to the Polynesian community at Williams's request.

"I had lunch with Sonny on Thursday and we spoke at length about our plans for 2009," Greenberg said. "I'm as shocked as anyone."

NRL chief executive David Gallop described the situation as "unacceptable". "It is unacceptable to walk out on a contract," he wrote. "If he has personal issues we are happy to discuss them with him. We will support the Bulldogs to enforce the contract and prohibit Sonny Bill from playing for any team other than the one he is contracted to."

News of Williams's decision was treated with disbelief in New Zealand. Former Manly fullback Matthew Ridge said: "It's pretty immature. I honestly can't believe this news. Sonny Bill appears to have changed from a fiercely loyal Bulldog to [someone] who is looking out for himself and the big dollars."

Former Wallabies coach John Connolly, who last week wrote in The Sun-Herald of the danger French rugby posed to the NRL said: "My first reaction was that it can't be true. Contractually it just can't happen unless someone at the club told him that yes, you can go or unless he hasn't been paid third-party money or something like that, it just can't happen.

"I think it is pretty bad form from Sonny Bill. These guys, these highly paid young guys, just seem to have a different set of loyalties and values. It's all about the dollar. Every manager worth his salt will be trying to get his player over there now."

Phil Gould, who has been criticised for warning the NRL of the possible loss of the likes of Williams to overseas, offered just one quote last night: "I told you so."