Klitschko (left) and Chisora had been due to meet on 11 December
Britain's unbeaten heavyweight boxer Dereck Chisora's fight with IBF and WBO champion Wladimir Klitschko has been rearranged for 30 April in Germany.
Chisora had been due to meet Klitschko in December but the fight was postponed because of an injury to the Ukrainian.
It had been expected WBA champion David Haye would seal a unification fight with Klitschko but this ends his hopes of meeting the 34-year-old in April.
"This news is a fantastic late Christmas present," said Chisora.
The fight between Klitschko and 27-year-old Chisora could now open up the possibility of fellow Londoner Haye taking on the Ukrainian's brother Vitali Klitschko, who is the WBC champion, in April or May.
But the rescheduling of Chisora's bout with Klitschko will complicate Haye's hopes of unifying the division as the 30-year-old WBA champion has vowed to retire before his 31st birthday in October.
Haye said he was gloomy about the possibility of fighting Wladimir Klitschko in the future.
"I'm done with the Klitschkos," said Haye in a statement. "I know I can retire later this year with my head held high, knowing I did everything in my power to make these fights happen."
The Klitschkos' manager Bernd Boente revealed Haye and Wladimir had been close to agreeing an April date, but negotiations broke down at the final hurdle.
Boente said the sides had agreed on the material aspects of the fight, including a 50-50 split of the revenue.
However, they could not come to an agreement on a date and site for the fight because of conflicting schedules between RTL, the German network that features Wladimir Klitschko's fights, and Sky, the British subscription network that televises Haye's bouts on Sky Box Office pay-per-view.
Still, Boente said he was confident the Wladimir Klitschko-Haye fight will eventually be made.
"I'm pretty sure the fight will happen. I'm very positive about it," he told ESPN. "We were close with all the details. It was really a question about the date and venue.
"We always have to bring RTL and Sky together as our main TV partners and then go from there. We hadn't gotten into details about US TV, but that would have been HBO or Showtime, and I would prefer Showtime."
Klitschko had the option of rescheduling the fight with Chisora immediately, but when the prospect of a much more lucrative fight against Haye arose, the sides began negotiating.
"We wanted to do the fight on 30 April with Haye. We had two stadiums available in Germany, and coming to Germany was not a problem for Haye," added Boente.
"They only wanted neutral officials, judges, referee, all that. That is no problem. We agreed on all the points, but the major issue was Sky was not willing to do a second pay-per-view in April."
Boente said the earliest date for the fight they could come up with that suited the networks and tallied with venue availability was 2 July.
Both sides were willing to fight on that date, Boente said. However, he added that Haye and manager/trainer Adam Booth refused to allow Klitschko to take the 30 April interim fight with Chisora.
"They would not accept that, but Wladimir was not willing to wait another six months and have it be 10 months since his last fight against Sam Peter [in September]," Boente said.
I was gutted when Wladimir pulled out of our fight just a couple of days beforehand. But now I've got another chance to take his titles away.
Boente said Haye could also have taken an interim fight and then faced Klitschko on 2 July.
Boente informed Chisora's promoter Frank Warren that they were rescheduling the fight under the terms of their original contract. The fight will take place at the SAP Arena, where it was originally scheduled.
"I always believed that I would fight Wladimir Klitschko, and my faith has been repaid," added Chisora, the British and Commonwealth champion.
"I was a bit worried that he might try and fight an easier touch, but I think I've earned my opportunity.
"I was gutted when Wladimir pulled out of our fight just a couple of days beforehand. But now I've got another chance to take his titles away.
"He's a great world champion, but his time at the top is well and truly up.
"My promoter Frank Warren has done a great job in getting me this opportunity because there was no guarantee Wladimir would fight me again after he got injured."