Tyson Fury and Deontay Wilder's trilogy fight has been thrown into serious doubt amid claims the British champion has tested positive for Covid.
The two heavyweight fighters are set to face off on July 24 in Las Vegas, with preparations fully underway.
However, ESPN on Thursday claimed the bout could be pushed back until September after a positive Covid result in Fury's camp.
AP reported on Friday morning that Fury has tested positive, though it remains unclear if that is in addition to the previously reported positive reading.
Promoters Top Rank said they were monitoring the situation closely, with an announcement expected later on Friday.
"As soon as we have word, we will be putting out a statement," Top Rank media relations director Evan Korn told the PA News Agency.
Fury beat American Wilder to become WBC heavyweight champion in February last year, 14 months after the two men fought a thrilling draw.
The Briton has been training in Las Vegas in preparation for their third contest.
Fury, 32, had looked set to be heading into an all-British heavyweight showdown against Anthony Joshua in Saudi Arabia during August.
However, a legal ruling in the United States wrecked those plans, with an arbitration hearing upholding claims from Wilder that he was contractually owed a third fight with the WBC champion.
