NEW YORK – Representatives for middleweight contender Sergiy Derevyanchenko have sent a letter to the IBF demanding that the sanctioning body immediately order a mandatory title fight between Derevyanchenko and Gennady Golovkin.

A copy of the letter, sent Wednesday evening, was obtained by Yahoo Sports.

Golovkin, the IBF/WBC/WBA middleweight champion, was scheduled to face Saul “Canelo” Alvarez on May 5. That fight was canceled when Alvarez, facing a suspension from the Nevada Athletic Commission for testing positive for Clenbuterol last month, withdrew from the fight. Alex Dombroff, an attorney for Derevyanchenko’s promoter, Lou DiBella, wrote that because Alvarez-Golovkin was the WBC’s mandatory challenge for Golovkin, the IBF mandatory must be considered due immediately.

“Following Mr. Derevyanchenko earning the mandatory position in August 2017, we were informed in a series of phone calls with the IBF that, as a result of Mr. Golovkin holding the WBA and WBC middleweight titles in addition to the IBF, the timing of Mr. Golovkin’s obligation to fight Mr. Derevyanchenko would be subject to a rotation agreement in place between the three sanctioning organizations,” Dombroff wrote.

“As has always been discussed, Mr. Golovkin’s mandatory in the IBF would be due in the rotation system after his WBC mandatory was satisfied. At this moment, the WBC’s mandatory has been satisfied and expedited negotiations should begin for a bout immediately between Mr. Golovkin and Mr. Derevyanchenko. By immediately ordering that Mr. Golovkin satisfy his mandatory obligation by fighting Mr. Derevyanchenko, the IBF will not just be making the proper decision pursuant to its rules, but also shall ensure that its title and the boxers in its ratings are not held hostage.”

Golovkin (37-0-1) still intends to fight on May 5 in Las Vegas. The frontrunner to face him is Gary O’Sullivan, a source familiar with the fighter’s thinking tells Yahoo Sports. O’Sullivan (27-2) is coming off a knockout win over Antoine Douglas last December in a fight that was broadcast on HBO. HBO Pay-Per-View is expected to broadcast Golovkin’s next fight.

The Ukrainian-born Derevyanchenko (12-0) is even more of an unknown than O’Sullivan. An accomplished amateur, Derevyanchenko turned pro in 2014, and has fought exclusively in the United States. In the letter to the IBF, Dombroff said DiBella had already been in contact with Golovkin’s promoter, Tom Loeffler, and “made clear our willingness to complete a deal in short order on reasonable terms with GGG Promotions for Mr. Golovkin’s next bout.”