Anthony Joshua's world heavyweight title defence against Kubrat Pulev will be postponed by several months due to the coronavirus pandemic, Pulev, the IBF's mandatory challenger said on Thursday.
As of Thursday, promoters were still hopeful the fight will happen as planned.
The 38-year-old former European amateur super-heavyweight champion Pulev said the fight would probably take place at the end of the year instead of June 20 at Tottenham Hotspur's stadium in London as scheduled.
The 62,000 seater stadium was no longer available after European football's governing body UEFA postponed the European Championship to 2021, which means that any rescheduled Premier League fixtures could now run into the summer.
"It is impossible for the fight to take place on June 20, although I am ready," Pulev, known as "The Cobra" said. "The match will take place a few months later, perhaps towards the end of the year."
Pulev, one of Bulgaria's most popular sportsmen, challenged for the IBF world heavyweight title in 2014, losing to Wladimir Klitschko in Hamburg on a fifth-round knockout.
Joshua last fought in London in September, 2018 when he beat Alexander Povetkin at Wembley Stadium.
The flu-like virus that originated in China late last year has killed nearly 10,000 people and infected more than 235,000 globally. It has forced the cancellation or postponement of numerous sporting and other events.