Kell Brook is set to face Brandon Rios in London on September 12 after sliding out of contention to face Floyd Mayweather Jr on the same night in Las Vegas.
WBC-WBA-WBO world welterweight champion Mayweather (48-0, 26 KOs) said last week that fellow Americans Andre Berto (30-3, 23 KOs) and Karim Mayfield (19-2-1, 11 KOs) are possible opponents at the MGM Grand on September 12.
Sheffield's IBF title-holder Brook (35-0, 24 KOs) holds the only world welterweight title belt not in Mayweather's hands and has been on a shortlist of potential opponents, along with his fellow Briton Amir Khan and American Keith Thurman.
But with Mayweather's surprise announcement that Mayfield and Berto are front-runners for what he has previously claimed will be the last fight of his career, Brook's promoter Eddie Hearn is making other plans.
"We would love to make the Mayweather fight for Kell on September 12 and we are in the hat because Kell's world champion and if Mayweather wants to become undisputed champion with all the belts he has to take that fight.
"I don't think we will get it and others have been mentioned. Kell Brook is more creditable than the names that have been mentioned and like I said Mayweather could have the chance of unifying the division, but I don't think it will happen.
"We are going for Kell's next defence to be at the O2 Arena on another huge show there and it's looking like it will be against Brandon Rios."
Hearn also expects new IBF featherweight champion Lee Selby to make a first defence in Cardiff on September 19.