Tyson Fury and Anthony Joshua must fight before the end of the year, according to promoter Frank Warren.
The two heavyweight world champions are on a collision course which would see all four belts on the line.
Fury won the WBC strap by stopping Deontay Wilder last month while Joshua won back his three belts by beating Andy Ruiz Jr in their rematch.
Fury must beat Wilder again this summer after the American triggered his rematch clause while Joshua is due to take on Kubrat Pulev at Tottenham Hotspur Stadium on June 20.
Assuming they emerge unscathed, Fury and Joshua could clash in December with Saudi Arabia the leading contender to host the fight.
But Warren, who represents Fury, warned that if the fight does not happen in 2020, it could be lost for good.
‘It’s got to happen and it’s got to happen this year," he told BT Sport.
"To get that fight on, everybody involved has got to sit around a table and get it hammered out.
"It will happen providing Kubrat Pulev doesn’t knock out or stop Joshua. You make AJ favourite [against Pulev] but in his last few fights he’s been caught. Everyone fighting him now knows what they need to do to win.
"Of course I’m optimistic, providing everyone keeps winning. ‘But it will only get done if everyone sits down and makes it happen.
"Those two fighting will be the biggest sporting ever this country has seen since England won the World Cup.
"I’d like to see it be held in the UK, but it depends on the money. Fury is the best heavyweight of his generation. Never lost a fight. He’s the number one."
