Alkass Digital
Anthony Joshua will fight at London's O2 Arena as planned on Saturday, with promoter Eddie Hearn set to announce Dillian Whyte's replacement imminently.
Whyte returned "an adverse finding" from a doping test last week, meaning the heavyweight rematch was cancelled.
A "devastated" Whyte, 35, said he was "completely innocent".
Hearn told BBC Radio 5 Live: "I believe that fight will be signed and an announcement made on Monday night or first thing in the morning."
He added: "The absolute plan is to have a show on Saturday night. It's a minefield because everyone puts their name in the hat and the credible ones want £10m, a private jet and my left lower limb in the contract."
Joshua, 33, reacted "calmly" to the news of the cancellation of the fight after the Voluntary Anti-Doping Association (Vada) informed promoters Matchroom and boxing authorities of Whyte's test result.
"With a week to go before one of the biggest fights of the year I was shocked and dumfounded. AJ sent me a message which was unbelievably calm," said Hearn.
"AJ is desperate to fight. He has looked unbelievable in camp. I have never seen him in such good shape.
"The plan is to get the most credible opponent and someone who can test him for Deontay Wilder.
"At this point, with such short notice, you need more than one plate spinning because people will try to disrupt things or outprice themselves. We have the guy who we think is the right guy, and others who are waiting as well."
The fight between Joshua and Whyte, a rematch of their 2015 bout, was announced in July.
Joshua knocked out Whyte in the seventh round of their heated British title fight eight years ago, which also took place at the O2, as he avenged a loss to his rival on the amateur circuit.
Whyte, who lost his only world title challenge to Tyson Fury in 2022, beat Joshua by decision as an amateur in 2009 to start what became a bitter rivalry.
Olympic gold medallist Joshua went on to become a two-time world champion.