Francois Botha has arrived in Australia and promptly ridiculed Sonny Bill Williams ahead of Friday night's heavyweight boxing clash in Brisbane.
Botha said Williams had "big balls" to take him on but suggested the former All Black was living in fantasy land about his boxing skills.
The rugged veteran South African believes his experience will be too much for the code-hopping Williams who has just five fights to his name.
Williams has never needed to go beyond six rounds to remain undefeated and now faces 12 rounds - if it goes the distance.
The 44-year-old Botha is no stranger to that length of fight during his 60-fight professional career that featured tangles with the likes of Mike Tyson, Lennox Lewis, Wladimir Klitschko and Evander Holyfield.
"He's got a lot of big balls, and I don't mean rugby balls," Botha told Australia's Courier-Mail, providing the sort of trash-talk promoters dream of.
"Why is he taking this chance? He should stick to rugby because I will hit him so hard that when he tries to catch the ball, he'll just miss it.
"Sonny should have fought my son, my son would kick his arse and he's not even a professional.
"I don't know what planet he (Williams) is from but I don't think he's from planet Earth."
Williams says it's time to take a bigger challenge in his boxing career but Botha warns that could backfire.
"In real life, he should never have an opportunity to fight a guy like me with just five fights to his name," he said.
"I'm only taking this fight because of his notoriety in rugby."
Williams is about to relaunch his rugby league career with the Sydney Roosters in the NRL after winning a rugby World Cup with the All Blacks, Super Rugby title with the Chiefs and dabbling in the lucrative Japanese rugby scene.
Williams' stable-mate Quade Cooper will make his boxing debut on the undercard.