Anthony Joshua's 'world heavyweight title defence against Kubrat Pulev, scheduled for June 20, has been postponed due to the coronavirus pandemic.
Britain's unified champion was set to face Pulev at the Tottenham Hotspur Stadium, live on Sky Sports Box Office, in his first fight in the UK in two years.
A new date for the fight, and the possibility of staging it at the same venue, is still being worked on.
"We're speaking to Tottenham, we've postponed the 20th date," promoter Eddie Hearn told Sky Sports. "We are working with them for dates in July and early August as well, when we hope we'll be back.
"Hopefully we see that fight take place at the end of the summer."
Bulgarian Pulev is the IBF mandatory challenger for Joshua, who also holds the WBA 'super' and WBO titles.
Hearn previously warned: "You will see one of the best AJ performances - the shackles are off from the Andy Ruiz Jr 2 fight in terms of being disciplined and following a game-plan.
"He can be more destructive in a better stand-up fight.
"The mind-set is the same and has been the same since day one, with a couple of tweaks. The Ruiz Jr defeat taught him not to be influenced by outside noise. Stay focused, look after yourself, be selfish.
"He gave time to everybody but this is an unforgiving sport and you've got to look after No 1. He did that for the Ruiz Jr rematch and he will do it again.
"He's been working since the Ruiz Jr rematch. There hasn't been a week where he hasn't been in the gym working on tactics, ability and technique. He's absolutely driven to be the best.
"This isn't a guy who fights then goes on holiday to have a few pints and a couple of pizzas, taking three months off with the kids. He is working day-in day-out. He's an absolute role model to any athlete and any individual in sport.
"The Pulev fight is the focus. He has said: 'You make plans, for me it's only about Pulev'."
Joshua is eyeing an undisputed heavyweight title fight against Tyson Fury in the future. Fury shares a US promoter, Bob Arum, with Pulev.
Hearn said: "I sent [Joshua] Bob Arum's interview where he said 'there will be no AJ after Pulev knocks him out'.
"I did that to spark the flames in AJ.
"We need that. You've got to be up for this. Against Ruiz Jr the first time, maybe one of the problems was that the spark wasn't there. If you take your eye off the ball you will get beaten. With what's ahead, we can't afford to lose. He's doing everything to put an unbelievable performance together."