Bulldogs NRL star Sonny Bill Williams has switched codes and signed with French union side Toulon, the Top 14 club has announced.

"Sonny has joined us for one season with the option of another season," Toulon's president Mourad Boudjellal told AFP by telephone from Florida from where he has overseen the Aussie player's arrival.

According to Boudjellal, Williams "has confirmed his complete desire to finish with Rugby League to switch over to Union".

"He'll be at the very least in the stadium, or better on the team sheet" for Friday's friendly against Hyeres, he added.

New Zealand rugby league international Williams walked out on a five-year contract with Australian NRL club the Bulldogs to join Toulon and his abrupt departure caused a stir in Australia.

The Bulldogs, with the NRL's support, are attempting to legally enforce the 22-year-old's contract and prevent a feared mass exit of the game's elite stars to cashed-up European clubs.

But Boudjellal appeared unfazed by the threat of legal action.

"Our problem is: Is Williams under contract with another rugby union side? The answer is no," Boudjellal said.

"Therefore he's free to join with whoever he wants, he doesn't need a letter to leave."

Williams, who was in Toulon on Monday for the traditional medical, was described by the Toulon boss as "very serene, very determined to make his entry into rugby union".

"I can't see him going back to league," Boudjellal, who reckons his new signing could develop into an "extra-terrestrial" in rugby union, added.

"That seems to be a closed chapter in his career."

Not everyone in France is entirely happy with Williams' decision to jump ship from league with Serge Blanco, whose Ligue Nationale de Rugby controls the Top 14 and second division competitions in France, saying it was important players honoured their contracts before relocating to France.

"In my view, (Williams) should finish his season with his club in Australia and then come to France," Blanco told last Friday's The Sydney Morning Herald from Paris.

"I find it funny and bizarre that a player would break his contract in the middle of the season to go somewhere else.

"There is a rule in the French competition that a player can finish his season in Australia and then come to France midway through the season."

And NRL chief executive David Gallop has sought direct intervention from European rugby authorities - as well as the Australian justice system - to force Williams to return to the NRL.

The International Rugby Board's head of communications Greg Thomas said the matter was the concern of the Federation Francaise de Rugby, and not the game's ruling body.

"At a basic level, we don't believe anybody should break their contract," Thomas told the newspaper.

"We have heard from David about this matter, but it is really something for the French authorities."

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