Anthony Joshua-Wladimir Klitschko on for April in London -- sort of

The plans are in place, so now all heavyweight world titleholder Anthony Joshua has to do is win to make a much-anticipated megafight with former world champion Wladimir Klitschko a reality.

England's Joshua will defend his belt against American Eric Molina, a gargantuan underdog, on Saturday (Showtime, 5:30 p.m. ET) at the Manchester Arena in Manchester, England, and if he is successful, Joshua-Klitschko is on.

The fight is agreed to and, pending a Joshua victory, would take place on April 29 at Wembley Stadium in London, Klitschko manager Bernd Boente told ESPN on Monday.

Boente and Joshua promoter Eddie Hearn of Matchroom Boxing have been working on the fight since Tyson Fury, who is dealing with substance-abuse and mental-health issues, pulled out of an Oct. 29 rematch with Klitschko and vacated his title belts.

"We have reached an agreement for the fight and everything is fine. Eddie and I have had very smooth and constructive negotiations from the beginning," Boente said of the bout that would be for Joshua's title as well as one of the belts Fury vacated. "The only thing that is still being negotiated is a few details Eddie and I working on with the stadium, but it looks very positive. We have a deal together, but the most important step now is that Anthony Joshua wins his title fight on Saturday."

Klitschko, who once had Joshua as a sparring partner in his training camp, and Boente plan to be ringside in Manchester. If Joshua wins, Joshua-Klitschko could be announced after the fight, Boente said.

"Eddie and myself are co-promoters and we are working on everything together every step of the way," Boente said. "We are discussing certain things [about the announcement] and hope we can announce it then or next week. We are still discussing how to do it, but we don't want to be too premature. Joshua still has to fight, but if he wins, the fight with Wladimir is one of the biggest fights in years."

A fight between Joshua, a major star in England, and Ukraine's Klitschko, who has sold out stadiums across Germany, where he has fought for most of his career, indeed would be the biggest bout in the heavyweight division. It would pit Olympic super heavyweight gold medalists -- Klitschko in 1996 and Joshua in 2012 -- in a fight that many believe would challenge the British attendance record set by the rematch between super middleweight titleholder Carl Froch and British rival George Groves, who drew some 80,000 to Wembley Stadium in May 2014 for a fight Hearn also promoted.

"It's not important when we announce it. Our deal is made," Boente said. "We just have to sign it and wait until Anthony Joshua has done his work and hopefully beaten Molina, but Molina is a tough guy. He looked pretty good until he got knocked out by Deontay Wilder."

Wilder defended his heavyweight belt against Molina by ninth-round knockout in June 2015, although Molina has won both of his fights since by knockout.

What if Joshua (17-0, 17 KOs) were to lose to Molina (25-3, 19 KOs) on Saturday?

"If it happens, then we have to deal with it," Boente said.

But he added that Klitschko (64-4, 54 KOs), who will turn 41 in March and will have been out of the ring since Fury ended his nearly 10-year title reign in November 2015, thought Joshua would come through the fight in strong fashion and that he looked forward to fighting in England.

Klitschko has fought once previously in England, a seventh-round knockout of Monte Barrett on a Lennox Lewis undercard in 2000. It was Klitschko's final fight before winning his first world title three months later.

"Wladimir is fine that the fight is in the U.K. because he loves the challenge and he loves that everybody in the stadium will be against him," Boente said.

Boente added that Joshua, 27, and Klitschko have agreed to have drug testing for the fight to be overseen by the Las Vegas-based Voluntary Anti-Doping Association, which was overseeing drug testing for Fury-Klitschko II when Fury twice tested positive for cocaine.