Sonny Bill Williams will be prevented from playing rugby league in Australia again should he place just one toe on a rugby field in France, NRL chief executive David Gallop has warned.

Apart from threatening that "the door will be closed" on a return to the NRL if the Bulldogs superstar accepts a two-year deal with French rugby powerhouse Toulon, an angry Gallop also described Williams as "troubled" for walking out on his teammates.

And Gallop has put the heat on the International Rugby Board to intervene, claiming the future of both codes depends on their response because Williams is breaking his contract. "The clear message out of this is the damage rugby can do to both codes," he said. "If they condone this, they are condoning a form of international piracy. I'll be calling on the IRB today to get involved on an urgent basis … They've got an interest to ensure that when players sign contracts, some stability to that is important to all codes."

An IRB spokesman declined to comment when contacted by the Herald last night because they were unaware of Gallop's remarks. The NRL were expected to write to rugby's ruling body this week.

"They have control over the member nations and they can surely get involved to stop the registration of any contract in France," Gallop said.

He insisted Williams's apparent defection was different to that of Dragons captain Mark Gasnier, who has enacted a clause in his current deal to sign a two-year deal with Stade Francais. Williams is set to walk out in the second season of a five-year deal signed midway through 2006.

Gallop yesterday held crisis talks with Bulldogs chief executive Todd Greenberg and assured him the NRL would assist the club to "pursue every legal option open to them" to stop Williams from playing elsewhere.

"If Sonny Bill were to play overseas, certainly the door would be closed on his returning to the NRL at any time in the future," he warned. "Let me repeat: it's far more fundamental than a question of contracts and money. This is about someone who has walked out on his teammates two days before a big game. Walking out on your teammates mid-season without notice flies in the face of why kids are encouraged to take up team sport."

Gallop admitted he was as stunned as anyone else when word filtered through on Saturday evening that Williams had boarded a plane bound for Europe.

Earlier this season, the two met in Gallop's office and discussed formulating programs to nurture the game's large Polynesian influence.

"Certainly he has done his reputation damage, not only in his own club but across all NRL players," Gallop said. "To make this type of decision, without talking to anyone within your club, knowing how your teammates might feel to be abandoned like this, indicates to me he is troubled.

"He's an adult. Whatever advice he's been getting, he has to make his own decision. And he has made that decision. I don't think we have to be blaming anyone else."

Gallop said league could not alleviate the drain of its players to European rugby union with a "quick fix". "It's very easy to articulate the challenges and the problems that the game has got," he said. "It's very difficult to come up with solutions that we will plug every hole. Large contracts are going to be on offer overseas.

"This sort of issue goes beyond the money and contracts and salary caps, it's about walking out on your teammates."