Sonny Bill Williams has breached an Australian court order by making his debut for French union club Toulon.
The New Zealander had been prevented from playing in Europe after he walked out on a five-year deal with rugby league side Canterbury without warning.
But the 23-year-old said he is willing to go to prison after playing in the friendly against Carque-Hyeres.
"If they want to send me to jail for what I believe, then so be it," he told the Sydney Morning Herald.
A huge roar from 3000 fans greeted his arrival on Friday evening, but just 10 minutes into Williams' union debut he was sin-binned for an illegal shoulder charge on his opposing winger.
The NRL - the country's top tier - has asked Europe's union authorities to force Williams to answer charges in Sydney.
"The evidence satisfies (Williams) has failed to attend to his contractual responsibilities," Judge Robert Austin had said at a hearing on Thursday.
The court papers were reportedly served on Williams by being thrown over a fence onto Toulon's training ground, but the player was not represented at the court hearing in New South Wales.
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"There have been numerous attempts to distract the game from the fundamental issue, which is that a contract is a binding commitment on the part of both the player and the club," said Gallop.
"It protects both parties and places responsibilities on both parties.
"The issuing of a NSW Supreme Court order in respect of those responsibilities should provide a stark reminder to Sonny Bill of the importance of him observing the terms of his contract.
"It is a very serious matter for such an order to be granted and anyone who breaks an order of the NSW Supreme Court would face contempt proceedings from that court."
Williams has defended his controversial decision as financial "common sense" and complained that the NRL clubs treat players "like cattle".
He has been named in New Zealand's preliminary squad for October's Rugby League World Cup pending the outcome of the court proceedings.
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