SBW a million dollar baby?

Wellington - Rugby star Sonny Bill Williams has been offered more than AUS$1.0 million to prove his boxing credentials against in-form Joseph Parker, whose camp taunted that he would run from the challenge "like a little girl".

Part-time boxer Williams, who holds the New Zealand Professional Boxing Association heavyweight crown, has been challenged to step into the ring with rising New Zealand professional Parker in a winner-takes-all bout.

"He will be relentlessly ridiculed if he doesn't step up to take this fight," Dean Lonergan, from Parker's promoters Duco Events told the Herald on Sunday.

Williams, who is expected to announce within the next week whether he will switch from rugby league to rugby union for the second time in his stellar career, has not yet personally responded to the offer.

The former All Black, who is currently playing for Australian National Rugby League finalists Sydney Roosters, has dabbled in boxing for several years without facing any top fighters in their prime.

He won the vacant New Zealand heavyweight title in early 2012 with a first-round knockout of unfit journeyman Clarence Tillman who was a late replacement when Williams' original opponent was arrested on drug-related charges.

Unbeaten Parker fights for the New Zealand Boxing Federation belt on Thursday.

Duco has been trying to flush out Williams ever since it signed Parker to its stable and Lonergan told Fairfax Media he was prepared to split the purse if Williams and his manager Khoder Nasser wanted a payday.

"But I'd say they will run like little girls, because they know they're going to get belted," he said.

Nasser, when contacted by the Herald on Sunday, was not impressed.

"Tell Dean Lonergan to get in line," he said.

"Tell him to get back down his burrow and not stick his head out too far.

"Tell him too about that old Chinese proverb -- be careful what you wish for."

The one opponent Williams and Parker have in common is veteran South African Francois Botha who Parker knocked out in the second round and Williams controversially beat on points over 10 rounds.

Botha's later claim that he was offered Aus$150 000 to throw the Williams fight was denied by Nasser.