Devon Alexander will not be allowed to try and unify the welterweight division against Floyd Mayweather Jr at the expense of Kell Brook, according to the International Boxing Federation.

Alexander and Brook were meant to fight for the former's IBF belt in Detroit on February 23, but the American withdrew on Monday citing a biceps injury.

Waters were then muddied on Wednesday morning when Mayweather Jr, the unbeaten pound-for-pound best boxer on the planet, claimed he was close to agreeing terms with Alexander for a unification fight.

"The negotiations for my fight are almost done. The front runner is IBF Champion Devon Alexander. It'd be a unification bout at welterweight," he told his official Facebook and Twitter pages.

A scrap with Mayweather Jr would be financially more beneficial for Alexander but, as the IBF champion, he has an obligation to fight their mandatory challenger Brook, who earned the right by beating Hector Saldivia in October.

The only way Alexander could have even tried for a unification fight with Mayweather Jr would have been to have got exemption from the IBF within 90 days of his last fight on October 20.

And according to them, that has not and will not be granted.

In a statement, they said: "We have not received any requests or information on this from either camp.

"Because Alexander is under contract to fight Brook he would not be granted an exception to fight Mayweather."

Brook's promoter, Eddie Hearn, promised to fight tooth and nail for Brook, the 26-year-old from Sheffield who has been in a 14-week training camp ahead of the proposed Alexander fight.

The unbeaten Brook said on Twitter that he was willing to face anyone in order to become a world champion, writing: "I have been in camp for 12 weeks I want to do damage. Alexander, a vacant belt or even Mayweather I don't care!"

The IBF's stance backs up the thoughts of Hearn, who has called on Alexander's promoters, Golden Boy, to show their hand.