Anthony Joshua and Kubrat Pulev's representatives have set a deadline of January 31 to agree their proposed heavyweight world title fight.
Joshua last month regained his IBF, WBA and WBO belts with a landslide points win against Andy Ruiz Jr, who scored a stunning stoppage triumph over the previously unbeaten Briton back in June.
It means there is once again a clamour for Joshua to take on the winner of a rematch between his compatriot Tyson Fury and WBC king Deontay Wilder next month but, as a unified champion, the London 2012 gold medallist has mandatory obligations to address.
Pulev, who was scheduled to face Joshua in Cardiff in October 2017 before withdrawing through injury, is the IBF's mandatory challenger, while former undisputed cruiserweight champion Oleksandr Usyk occupies the same status with the WBO.
At this stage, Pulev appears to be the frontrunner and an IBF spokesperson told Sky Sports: "I have just been told that the Pulev and Joshua camps have asked [for] until January 31 to negotiate."
In the meantime, Usyk looks set to take the opportunity to further acclimatise to the heavyweight division, with a London showdown against experienced former world-title challenger Dereck Chisora pencilled for late March.
Like Joshua, Usyk is represented by promoter Eddie Hearn and his Matchroom operation.
"Conversations are ongoing with all parties to plan what's next and it will really come to a head over the next few weeks," Hearn told Sky Sports.
"We are still awaiting clarification from the governing bodies to confirm who is chronologically next [for Joshua out of Pulev and Usyk] but right now everything is in play.
"In terms of Usyk versus Chisora that is still a potential outcome, but March 7 is unlikely. Instead we have March 28 on hold at the O2 Arena."
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