A fight between IBF world heavyweight champion Anthony Joshua and Wladimir Klitschko is "very close", promoter Eddie Hearn says.
On Wednesday, Briton Tyson Fury - who had withdrawn from two scheduled rematches with Ukraine's Klitschko - relinquished his WBA and WBO belts.
That leaves Britain's Joshua and Klitschko free to fight for the WBA and IBF titles in a unification bout.
"It is the big favourite to be the next fight for both," Hearn said.
He told BBC Radio 5 live that he thought both men would be "going to the gym now everyday focusing on each other and that fight being next".
He added: "Whether it gets over the line time will tell. It is the biggest heavyweight fight in the last 10 years. I want to get it over the line."
Unbeaten Joshua, 26, was scheduled to defend his title on 26 November in Manchester, but Hearn says a fight with Klitschko, 40, would most likely be held on 10 December, probably in Manchester or London.
Fury beat Klitschko last November to win the WBA, IBF and WBO titles.
Within two weeks the Briton was stripped of the IBF title because he was unable to fight mandatory challenger Vyacheslav Glazkov.
Fury, who has admitted he has been taking cocaine to help him deal with depression, relinquished his remaining two belts on Wednesday.