Promoter Eddie Hearn has said that Cardiff is the "frontrunner" to host the rematch between Andy Ruiz Jr. and Anthony Joshua on Dec.14.
Ruiz knocked out Joshua at Madison Square Garden to win the WBA, WBO and IBF world titles in June with one of the biggest upsets in boxing history.
Neither a venue or date has been confirmed for the triggered rematch but Joshua's promoter Hearn is adamant the bout will take place.
"It's not even up for negotiation if he's taking that fight or not," Hearn told BBC 5 Live. "That fight is happening.
"Do you think Joshua wants a warm-up? No. Someone just asked me 'do you think he should be taking this fight?' I said 'probably not'. In an ideal world probably you'd like a 10-rounder.
"If you're a favourite for a fight for the heavyweight titles, you're taking that fight. It is risky, dangerous, dramatic but it's the biggest fight in world boxing."
Hearn added that prospect of the title fight being held at Cardiff's Principality Stadium was "tempting" due to its capacity of 80,000.
Joshua recently released a video explaining that Ruiz was not the man he wanted to fight going into the bout in New York last month.
The Watford-born fighter knocked Ruiz down in the third round before the Mexican recovered and put Joshua down four times to win the belts.