By Liam Napier

American boxer Chauncy Welliver is the favoured contender to fight Sonny Bill Williams on a Sydney card that will feature an all-star cast of fellow rugby and league stars late next month.

Fairfax Media understands Welliver, an experienced southpaw with a credible 55-10-5 record and who has spent time in New Zealand, is the preferred option of Williams' agent, Khoder Nasser.

Argentina's Nelson Dominguez (17-4-1) is another potential candidate but Welliver's local appeal may hold sway.

NRL star Paul Gallen, Wallabies playmaker Quade Cooper and All Blacks flanker Liam Messam, who may make his pro boxing debut, are also likely to be drawcards at the same event, before their respective rugby and league seasons begin.

Nasser and Williams are expected to hold a press conference in Sydney today to confirm the 29-year-old's return to the ring - and reveal his opponent.

In another twist, the fights are likely to be screened in Australia on a free-to-air network in order to counter the saturated pay-per-view market.

While Welliver comes off three successive losses, the last two were against undefeated Australian Lucas Browne (21-0) and Alexander Ustinov (30-1) - the Russian giant who sent David Tua into retirement last year.

Welliver has also been active, fighting three times this year.

The 31-year-old is a former New Zealand heavyweight champion who has fought 413 professional rounds and was once ranked in the top 15 by the World Boxing Council and World Boxing Organisation.

In what will be Williams' seventh fight, Welliver offers a genuine test and appears to tick all other boxes.

"A fight with a guy like Sonny Bill Williams, who I respect, is a big fight for me," Welliver told Fairfax Media from Las Vegas.

"I'm at the point in my career where I'm not going to get a fight with Klitschko.

"This is something I'm taking extremely seriously.

"I'm extremely excited about the potential of fighting Sonny Bill Williams."

Williams' last fight - a controversial points' win over South African veteran Francois Botha almost two years ago - was marred by claims the contest was shortened from 12 to 10 rounds.

"In a street fight Frans Botha won that fight," Welliver said.

"He got the last of it but people forget for eight rounds Sonny Bill Williams boxed masterfully against a guy with 10 times his experience.

"Yes Sonny Bill got his butt kicked for two rounds but he dominated for eight rounds.

"I know that because I've been studying the tapes this past week.

"I thought he was a pretty boy; a star, but he weathered the storm even though he had to hold on like it was his prom date.

"He made it through and Frans Botha is no mug."

Welliver has been drastically overweight in his recent bouts but he claims the hype surrounding Williams presents the perfect motivation to get in shape.

"I want to look good on TV.

"At this stage of my career it doesn't get any bigger than this," he said.

"I think I'd have too much experience. Fighting a superstar is huge motivation. I'm fighting someone more popular than Klitschko.

"This is my time to shine. I know a fight with Sonny Bill Williams puts me in line to fight Joseph Parker.

"I know he puts me in a good spot.

"I'm in a no lose situation.

"I've been there done that. He's not going to take away my 'legacy'.

"Sonny Bill has accomplished a lot for his limited time in boxing but he is still a little boy. The older man will outsmart the little boy."