Paul Gallen wants to fight SBW
Gallen (4-0) and Williams (7-0) both remain undefeated in the heavyweight boxing division, however busy schedules in their chosen rugby codes have meant a bout has been almost impossible.
"We're talking about it but I suppose it's just hard to line our two schedules up," Cronulla forward Gallen told Fox Sports News.
"I suppose if it doesn't happen in the next 18 months, it's probably not going to happen.
"Hopefully this time next year or in 18 months it might happen."
A fight between the pair would be a guaranteed crowd-puller and TV ratings would also likely be through the roof.
Both have been amongst the top rugby league players over the past decade - and often controversial figures - while All Blacks World Cup-winner Williams has also made a big impression in the 15-man game.
"I think Sonny Bill Williams is the end game, to be honest," Gallen said.
"I wouldn't say I've got visions of becoming a world champion or even an Australian champion.
"But when I had my first fight, three or four years ago, everyone said oh, you need to fight Sonny Bill."