Mark Hunt couldn't wait until Wednesday night to take a swing at Paul Gallen, throwing a punch during their heated weigh-in.
The pair are featuring in the co-main event before Aussie Tim Tszyu fights Kiwi Bowyn Morgan in Sydney, and the bad blood spilled over as things turned feisty just a day out from their blockbuster battle.
Unprovoked, former UFC star Hunt shoved Gallen in the chest then later broke free from his entourage and threw a left hook at Gallen, who didn't flinch.
"Mark Hunt has just thrown a punch at Paul Gallen at the weigh-in. Hunt very annoyed by Gallen's talk," Daily Telegraph reporter Jamie Pandaram wrote on Twitter.
Fox Sports journalist Cody Kaye tweeted: "Just spoke to Gallen and Hunt. That was legit. Neither planned it. I believe both."
Hunt weighed in for the heavyweight clash at a tick over 127kg and said the time for talking is over.
"Five years this has been in the making. He's been talking a whole lot of garbage, and now we're here," he said. "It's showtime for this guy, let's see if he can cut it.
"(His talk) increases my fire to put him to sleep."
Gallen, who tipped the scales at 103.66kg, laughed off Hunt's scare tactics but admitted he was "shocked".
"That's a bit shocking that," he said in response to his opponent's attempted punches.
"He's trying to intimidate me — we said from day one we'd be professionals, it'd be a respectful build-up, but that shocked me a little bit.
"As I've said from day one, I don't need any motivation ... I'm just here to get the win, go home to the family and have some fun for Christmas."
The incident comes after tempers flared at Monday's press conference when ex-NSW and Cronulla captain Gallen said he accepted the fight to "get paid" and told Hunt he "should have stayed in retirement".
Gallen added Hunt should be thanking him, because the 46-year-old wouldn't be earning such a lucrative payday if it wasn't for the former rugby league star putting on the gloves, but Hunt wasn't having it.
"This ain't footy, this is fighting," Hunt said. "I don't know where he gets his ideas, especially with the money side. He's talking s**t again.
"Wednesday's coming. I'm telling you, you're going to sleep."
Gallen is undefeated in 10 fights and has outclassed fellow footy stars including Anthony Watts, Bodene Thompson, Junior Paulo and John Hopoate.
His last fight, against AFL legend Barry Hall in late 2019, ended in a draw.