Joseph Parker is out of his fight with Dereck Chisora due to illness.
Promoter Eddie Hearn confirmed the news on social media on Wednesday, noting that he was working on a suitable replacement opponent for Chisora.
ESPN boxing analyst Dan Rafael said Parker had been ill for much of the week and unable to train, after suffering a spider bite.
"He [Parker] and his team believe it was caused by a spider bite - so he has withdrawn from a fight with Dereck Chisora that was scheduled to take a place on October 26 [Oct 27 NZT]," he said.
The fight with Chisora had been in the works for months, with April originally targeted, but stalling from the Chisora camp led to Team Parker pulling out of contract talks.
Once Parker signed a three-fight deal with Matchroom Boxing, Hearn was able to step in and get the fight made.
Chisora had already threatened to pull out of the fight himself, upset at not being the top billing on the card.
Parker and the 35-year-old slugger were schduled to play second fiddle to a super-lightweight title fight at London's 02 Arena.
"That's not gonna work for me," Chisora said at a recent press conference. "I'm not going to be chief support, that won't work for me.
"I'm not going to sell out O2 for them guys to be the main event.
"These guys wouldn't sell box office by themselves, so f**k that. Either you give me main event or pull me out of the f***ing show.
"I'm being serious, you want me to sell it out to the London crowd - my London fans - then put these little guys that no-one knows about on my show and mug me off.
"I'm taking the main stage - if not, I want more money. You can f**k off, I'll be walking away from this."
Just last week, Parker's trainer Kevin Barry revealed the former WBO champion had been put through the ringer during fight camp.
Chisora is known for his rough-house tactics - something Barry was preparing Parker for.
"I've actually got some very good sparring guys," Barry told Sky Sports UK. "I won't name them... one in particular, who is mimicking Chisora very well.
"Everything from leading with his head, using his elbows, and his forearms and low blows, and choking Joe with his arm, pushing Joe's head down. All the fouls that we know Derek Chisora has as part of his skill-set."