The NRL won't allow Sonny Bill Williams to sign a short-term contract towards the end of the season according to chief Daily Telegraph reporter and guru, Buzz Rothfield.

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The talk of the NRL town in the last few days has been whether or not SBW will return to the club where he won a premiership in 2013 after Big Sports Breakfast host Jimmy Smith said it was a done deal.

“Sonny Bill Williams will be turning out for the Roosters in season 2018," Smith said on the weekend.

"The mail is good. From what I understand the deal is done.

“It will be a short stint at the end of the Super Rugby season.

“They (the Roosters) would have to register the contract before June 30. They have space in the cap.”

From the start, Rothfield said there was no chance, and SBW confirmed via a text that he was happy in rugby union.

On NRL360, Rothfield and Paul Kent debated the potential signing and referred to Jarryd Hayne's similar move where he came back to the NRL in 2016.

"It's actually an old rumour that was around a month ago," Rothfield said.

"I rang Nick Politis then, spoke to a couple of other people and they were very strong in their denials.

"I'm still convinced now it's not going to happen.

"I spoke to Sonny Bill via text message, and he's determined to play in the (Rugby) World Cup in 2019.

"If he does come back to the Roosters, he'll be there on the coaching staff."

Kent asked whether there was the potential for a short-term deal after his season with the Auckland Blues is over in 2018.

"What intrigues me is if he gets to the end of this season of Super Rugby, which ends on October 4, and he says to the New Zealand Rugby Union, "I just want to go and spend the next eight weeks playing rugby league, earn a little bit of extra coin,' Kent said.

Rothfield shut that down very quickly.

"I checked that with the NRL today and said, "if he was to come back short-term, would it be like Jarryd Hayne could he do it after June 30?"

"They said, "under no circumstances would his contract be registered. If he wants to come back to rugby league, it has to be a long-term deal."

Jarryd Hayne signed for three years, and it appears the NRL isn't interested in letting SBW back into the competition unless he comes back for a longer period.