The World Boxing Super Series super-middleweight final between world champion George Groves and Callum Smith is unlikely to be held in the UK.
Groves, 30, and Smith, 28, won semi-finals earlier in the year.
The showpiece final - where Groves' WBA world title is on the line - will take place in September but tournament organiser Kalle Sauerland says it is "against the odds it is in the UK".
"I've heard rumours - Las Vegas, Middle East, lots of rumours," said Sauerland.
The World Boxing Super Series cruiserweight final between Oleksandr Usyk and Murat Gassiev is scheduled to take place in Moscow on 21 July, with all four world titles on the line.
As the tournament reaches the conclusion of its first season, the winner of each weight division will win any world titles on the line in their respective final and also walk away with the Muhammad Ali Trophy.
World champion Groves against the unbeaten Smith is highly anticipated for UK fight fans but speculation has intensified that the bout could take place in Jeddah, Saudi Arabia.
Sauerland refused to clarify a location but said the contest - already delayed while Groves overcomes a shoulder injury - cannot be put off much longer.
"That fight will take place in September and the venue is potentially outside the UK," Sauerland told IFL TV. "It's against the odds it's in the UK."
As part of the contingency plan in the event either fighter sustains injury before September, Sauerland confirmed Chris Eubank Jr - who lost to Groves in the semi-final - is still under contract as the only replacement.
"We have tried our very best to get the original fight on, pushing the date back," added Sauerland.
"But if there's an injury in training now it will be X against Eubank Jr."