Contrary to reports over the weekend, Warren says he has not signed the American for Hamed's 12th defence of the World Boxing Organisation featherweight title to take place in either Las Vegas, New York or Atlantic City.
"We are certainly talking to McKinney's people, but he is only one of three possible opponents," Warren said. "I don't want to name the others. I've heard that people are saying it will be held in Britain, but I'm looking at venues in the United States."
Warren was to have announced the fight at London's Dorchester Hotel on Sunday, but a late hitch apparently could not be overcome in time.
McKinney, from Memphis, caused a shock by stopping Junior Jones to win the WBO super-bantamweight title in December.
Jones had already signed to challenge Hamed, but that defeat ruined the fight, and McKinney expected to move to the head of the queue to meet Hamed.
McKinney said recently: "They were going to give Junior Jones the shot if he beat me. I have a message for the Prince. We spoke to each other in New York about fighting each other and you said that if I beat Jones, I'd get the fight. Now it's put up or shut up."
Meanwhile, Warren reports that McKinney has been stripped of the WBO super-bantam title, which leaves Liverpool's No 1 contender, Richie Wenton, looking for another opponent to meet on 6 June.