Oleksandr Usyk says the buck now stops with Tyson Fury as it pertains to whether or not the boxing world will get to see the undisputed heavyweight championship.

Usyk, the WBA, WBO, IBF, IBO heavyweight champion from Ukraine, has offered a stern indication saying he has exhausted all his efforts in his negotiations to strike a deal with Fury, the WBC titlist, for all four major heavyweight titles.

“The points for agreement were sent to Fury’s side,” Usyk tweeted on Saturday. “The deadline is set. The clock is ticking. The ball is on #Greedybelly’s side now. We did everything in our power to make it happen.”

Usyk’s remarks follow weeks of frustrating, helter-skelter talks between the two sides, marked, moreover, by public ultimatums issued by Fury. Negotiations initially appeared straightforward for a while, but last month, after it became clear the fight would no longer take place in the Middle East, the organizers have had to contend with a new financial reality, one that has seen Fury call for a 70/30 split in his favor. Usyk, who initially called for no less than a 50/50 split, accepted the new terms, but it only seemed to yield further disagreement

The promoters have penciled in the fight for April 29 at Wembley Stadium, but with time running out to announce the fight with sufficient lead time, Usyk’s representatives have either expressed doubt or threatened to pull out of the fight altogether.

On Thursday, Egis Klimas, Usyk’s promoter, suggested that if Fury’s promoters—Queensberry Promotions in the UK and Top Rank in the US—are unable to come through with an April 29 date for the fight, Usyk would pivot to a mandatory defense of his WBA title against British contender Daniel Dubois.

In a follow up tweet on Saturday, Klimas reiterated his charge’s claim that they had assented to all of Fury’s various demands, while offering what appeared to be a racial slur. Klimas has indicated previously that his team was trying to retain the services of a UK-based legal firm to assist with negotiations.

“We bend enough to make this happen, Fury always wanted his way, we allowed it to some point and now let’s see if “Gipsy King” is man enough to take this fight, sorry for us he is not a King, just a gipsy…” Klimas wrote.