Wladimir Klitschko is the IBF, WBO and IBO champion
Wladimir Klitschko has confirmed Ruslan Chagaev as a replacement opponent for British heavyweight David Haye.
The IBF, WBO and IBO champion was due to face Haye in a 60,000 sell-out at Schalke 04 FC's Veltins Arena.
Haye had hoped that the fight could be restaged three weeks later after withdrawing from the original date with a back injury sustained in training.
But Ukrainian Klitschko was keen to retain the date and will face joint WBA champion Chagaev instead.
Problems with television broadcasters and further doubts over Haye's fitness also helped convince the Klitschko camp to draft in the 30-year-old.
"It's unfortunate that David Haye can't compete. But now I'm looking ahead and I'm excited about a particularly sporting challenge with Ruslan Chagaev," said Klitschko.
The Uzbekistani, unbeaten in 26 fights, shares ownership of the WBA crown with Russian Nikolai Valuev.
A title decider between the pair has been delayed three times with the WBA's deadline for a meeting due to expire at the end of this month.
Klitschko's coach Bernd Boente has claimed that the winner of the fight between Klitschko and Chagaev will be classed as heavyweight champion in the Ring magazine's respected rankings.
"We have already waited until June [to fight Haye] when we wanted to fight March, April," explained Boente earlier this week.
"We don't know if Haye will really be ready on 11 July. It could be that he hurts his back again and we have the same problem.
"The important question is are RTL happy to go on 11 July? Are HBO ready to go three weeks later?"