Eddie Hearn, who promotes Tony Bellew, was attempting to finalize a deal for a year-end showdown with IBF, WBA, WBO, WBC cruiserweight world champion Oleksandr Usyk.
But now the contest is in serious jeopardy of being pushed back to 2019 - after the World Boxing Association ordered Usyk to make a mandatory defense against Denis Lebedev.
The scenario is reminiscent of what transpired a few months ago - when the WBA ordered Anthony Joshua, who Hearn also promotes, to make a mandatory defense against Alexander Povetkin - as Joshua was negotiating a unification with Deontay Wilder. Joshua faces Povetkin on September 22.
Lebedev was the WBA's champion at the weight, but due to inactivity the sanctioning body made him the "champion in recess" earlier this year, and elevated mandatory challenger Yunier Dorticos to the status of full champion.
Dorticos was then knocked out by Murat Gassiev, who took control of the title. And then in July, Gassiev was dominated over twelve rounds by Usyk in the final bout of the World Boxing Super Series cruiserweight tournament.
According to Hearn, Bellew is not interested in facing Usyk unless all four of the world titles are at stake. In order words, if Usyk drops the WBA title or the sanctioning body refuses to approve the bout - Bellew will not go forward with the contest.
"The only way that Usyk versus Bellew happens is if all the belts are on the line," Hearn told Sky Sports.
"We will have to see what happens but certainly yesterday's news means Usyk versus Bellew is unlikely for 2018."
Speaking last week, Usyk's promoter Alexander Krassyuk had welcomed a battle with Bellew in Britain.
"Usyk has become Olympic champion in England and he is looking forward to defending all of his four belts," Krassyuk told Sky Sports. "That will be a great honour for him and his team."
The situation is very odd - considering the fact that Lebedev is scheduled to fight Hizni Altunkaya on September 7 in Russia. It will be Lebedev's first bout since July 2017.