Rugby league star Paul Gallen doubts his much mooted boxing bout against Sonny Bill Williams will ever take place.

Gallen said there had been talk of a fight against dual league and union international Williams since the Cronulla skipper had his first professional fight almost three years ago.

Williams' hectic sporting career was put on hold after he ruptured an Achilles tendon playing rugby sevens for New Zealand at the Olympics in August.

"He's obviously out a fair while ... but it's sort of getting to the stage now, is it going to happen or not?" Gallen said.

"Everyone wants to see it, I've said I want to do it. Someone make it happen."

The 35-year-old Gallen climbs back in the ring on Friday night at Sydney's Hordern Pavillion against a fellow NRL player, Canberra prop Junior Paulo.

The Sharks, New South Wales and Kangaroos forward scaled 103kg, 18 lighter than Paulo at an unofficial weigh-in on Thursday for their charity heavyweight bout.

Paulo, who will make his boxing debut, will also enjoy a significant height difference over Gallen.

'"It's a big weight advantage, but you've got to be able to use it," said Gallen, who has won all five of his professional bouts.

"The size advantage doesn't worry me one bit. The biggest danger is him catching me with a good punch and knocking me out. It's the only chance he's got to beat me."

Paulo admitted it would be a big ask to beat Gallen despite the physical disparity.

"I've got to come out and fight a lot smarter than his past opponents have,' Paulo said. "I'm more excited than anything but I'm sure tomorrow night there will be a few nerves floating around."

Gallen said he bore no animosity toward Paulo, but made it clear he harboured ill feelings toward Ryan Carr, who he is scheduled to fight at Cronulla on December 23.

Carr labelled Cronulla "a bit of a bogan suburb" and called Gallen "their head bogan" in a News Corp article.

"I have to put up with criticism all year round, but to offend the area I live in and all the people there, just felt it was really disrespectful to all of them," Gallen said.

"I won a grand final for them, I'm going to knock this bloke out for them."