The decision to postpone the IBF, WBO and IBO title contest was taken after Londoner Haye, 28, suffered an injury in training at his base in Cyprus.
The pair were due to meet in front of a 60,000 sell-out crowd at Schalke O4 FC's Veltins Arena.
Haye was hoping to become Britain's first heavyweight world champion since Lennox Lewis retired in 2003.
A short postponement may allow the fight to be re-scheduled but Klitschko's camp appears keen to fight on the allotted date.
"I'm speechless. We will have to get someone else in. I will take who ever it is," said Klitschko.
The Ukrainian's manager, Bernd Bonte, added: "They haven't given any detail on the injury but say Haye can't train. We will get someone else but I can't say yet who it will be.
"Ninety five percent of the fans who bought tickets did so because of Klitschko."
A possible alternative opponent for Klitschko could be WBA champion Nicolai Valuev, the 7ft Russian whose fight against Ruslan Chagaev on Saturday was cancelled when Chagaev failed a medical.
The build-up to the Haye-Klitschko bout had been mired in controversy over Haye's controversial behaviour when promoting the fight.
He attended media events wearing a T-shirt depicting him proudly holding aloft the decapitated heads of Wladimir and his elder brother Vitali.
Renaming Klitschko as "Bitchko", he also derided him as an embarrassment to boxing and rubbished his record.