Frank Warren, promoter for Tyson Fury, admits he would be "disappointed" if Deontay Wilder follows through on his promise to exercise a contractual clause for a trilogy fight in the summer.
Fury stopped Wilder in seven rounds on Saturday night, at the MGM Grand in Las Vegas, to capture the WBC heavyweight title.
Warren would have preferred to have his boxer go directly to a full unification fight with WBO, IBF, WBA, IBO world champion Anthony Joshua.
Warren says the contract is concrete - where there is no way out if Wilder insists on a third fight. The first bout ended in a controversial twelve round split draw in December 2018.
Warren recently spoke with Wilder's co-manager Shelly Finkel, who insists once-beaten puncher is confident he can knock Fury out in the third fight.
"I prefer to go straight to Joshua, but that is the contract," Warren said to BBC Sport.
"It has to be honoured unless we can reach some accommodation for him to step aside. We could pay him to step aside if he wants to do that, but that is his choice. It would be lucrative for [Wilder], but I have spoken to his manager and Deontay does believe he has the beating of Tyson, and he can knock him out. I don't believe that. I fancied Tyson to stop him before the fight at the weekend. If he insists on the fight, we're locked into it."
Warren would still want the Fury-Joshua unification in 2020 - with Joshua already slated to make a mandatory defense against Kubrat Pulev in June.
"I want it before the end of the year, provided Anthony Joshua does not get defeated by anyone else," Warren said.