"I am very sorry for this final cancellation especially for the fans, " said 34-year-old Klitschko.
If he wins he becomes a national hero by getting rid of Wladimir Klitschko.
Londoner Haye also predicted that Klitschko would become a forgotten man after he "knocked him out".
The 31-year-old Sosnowski withdrew after he was offered a world title shot against Vitali Klitschko.
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Klitschko, younger brother of WBC champion Vitali, improved his record to 52 wins and three defeats.
Klitschko won every round and first had Rahman on the deck in the sixth.
Still, Boente said he was confident the Wladimir Klitschko-Haye fight will eventually be made.
Haye said he was gloomy about the possibility of fighting Wladimir Klitschko in the future.
HBO-HD (1080i): Transporter 2 (6:30 p.m.), The Devil Wears Prada (8 p.m.), WCB: Klitschko vs.
"They (the Klitschko brothers) want a defining fight and David wants a defining fight, " said Booth.
Speaking later during the press conference, 32-year-old Klitschko repeated his promise to make Haye regret his words.
Klitschko got the verdict of the three ringside judges by large margins of 117-109, 118-108 and 116-110.
Boente said Haye could also have taken an interim fight and then faced Klitschko on 2 July.
However, any meeting between Klitschko and Haye would only happen after they fulfil their contractual obligations first.
But the 31-year-old Sosnowski will now fight for Klitschko's WBC heavyweight belt in Gelsenkirchen on 29 May.
"It's a tough, tough fight for Dereck because Klitschko is the best heavyweight in the world, " said Warren.
Haye is determined to press on with his plans to fight Klitschko and shake up the heavyweight division.
In 20-30 years time no-one will remember my T-shirt, they'll remember the day I violently destroyed Wladimir Klitschko.
It was Klitschko, he said, who inspired his return after the two met in a Los Angeles restaurant.
Two judges had Klitschko ahead at the time of the stoppage with one judge putting Williamson in front.
Vitali Klitschko is the current WBC heavyweight champion, while his younger brother Wladimir owns the IBF and WBO belts.
However Chisora insists he will not step aside for Haye after Wladimir Klitschko's withdrawal from their planned title bout.
And Costello added that the cancellation could be good news for people wanting to see Haye fight a Klitschko.
But Klitschko did not state whether that would be against Chisora or Haye.
Former undisputed cruiserweight champion Haye, 28, pointed to Klitschko's six title defences as evidence to back up his claims.
Haye had previously doubted Klitschko's ability to fight Chisora on 30 April and then meet him barely two months later.
Because of the Harrison fight I am already in training and suddenly here comes the once-in-a-lifetime chance to fight Klitschko.
"I told my brother, 'I want to fight Haye', but he said no, he wants to fight him, " said Klitschko.
The bout against unbeaten Chisora, 27, was originally scheduled for December but was postponed when Ukrainian Klitschko tore an abdominal muscle.
Williams, who lost a world title challenge against Vitali Klitschko the same year, handed prospect Airich, 29, his first professional defeat.
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