Anthony Joshua's world title fight against Wladimir Klitschko has been postponed until next year after the Ukrainian suffered an injury in training, promoter Eddie Hearn has confirmed.
The IBF champion will press ahead with a planned title defence at the Manchester Arena on December 10 but has been forced to seek an alternative opponent after confirmation of Klitschko's injury, reported to be to his calf.
The fighters had been waiting for the go-ahead to announce the fight for Joshua's title and the vacant WBA belt, with a decision over the latter having been delayed - it is now expected to be announced on Tuesday.
Klitschko lost his grip on the WBA 'super' title, plus the IBF belt now held by Joshua, when he suffered defeat at the hands of Tyson Fury last November.
Fury was stripped of the IBF belt days after that victory because of a rematch clause with Klitschko, and he also relinquished his remaining titles earlier this month just before his boxing licence was suspended by the British Boxing Board of Control ahead of an investigation into drug and medical issues.
"We've been in deep negotiations for a few weeks now waiting on the decision from the WBA," Hearn said. "I was made aware that Wladimir picked up a minor injury late last week but regardless of that, with just over six weeks to go until December 10, it's unrealistic to put together a fight of this magnitude and give it the full build up it deserves.
"There will be an official announcement on Joshua v Klitschko coming very soon but for now we are seeking a new foe for December 10 and building a huge card for Manchester.
"We decided with Bernd Boente [Klitschko's promoter] let's get this over the line now for March or April.
"Fans will hopefully get something official this week. The WBA are supposed to give their decision today [Monday] or tomorrow but I believe that is going to be positive for Anthony Joshua and Wladimir Klitschko. Once that is, I think we'll move forward and sign terms this week.
"We'll announce that fight for the spring and we'll be able to give it the build-up it deserves. We'll probably take it to a stadium as well but for now everything is fixed on December 10.
"There's quite a few guys from America calling him out and we have a big deal with Showtime as well. Guys like Bryant Jennings, Eric Molina, Jarrell Miller, all guys in the top 15. David Price is calling Anthony Joshua out but I am not sure he has done quite enough. He's been making some noise and they are two Olympic medallists in an Olympic year. Over the next 48 hours we'll make our decision I would think."
What seems sure to be a mouthwatering December 10 card already includes a world title fight for Kal Yafai, who will face reigning WBA super-flyweight champion Luis Concepcion.
Former world super-bantamweight champion Scott Quigg will also return to action for his first fight since losing his unification showdown with Carl Frampton, also at the Manchester Arena, in February.