(CNN) -- Wladimir Klitschko has issued a fresh challenge for Britain's David Haye to face him in a potential heavyweight unification bout on July 2.
The Ukrainian holds the IBF and WBO versions of the crown, while Haye is the WBA champion.
First, Klitschko must put both his titles on the line against another Briton, Dereck Chisora, in a rescheduled bout on April 30 and Haye has a mandatory defense against Ruslan Chagaev of Uzbekistan.
But a spokesman for Klitschko and his brother Vitali, who is the WBC heavyweight champion, said Wladimir wanted a summer bout with Haye.
"That's right, Wladimir is still up for July 2," Klaus-Peter Dittrich told CNN.
"He's emphasing once again he's willing to fight him on that date.
"We have initial agreements with TV channels and a stadium and would fight Haye in either Germany or Britain," he added.
Haye has threatened to quit boxing when he turns 31 in October and last month spoke of his frustration at landing a definite date for a bout with Wladimir Klitschko.
"Fight fans just want to see the best against the best -- if only it was that simple," Haye told Press Association, adding that it would be "impossible" to take on a July bout after fighting in late spring.
Meanwhile, the Klitschko brothers have announced that one of them will take on Tomasz Adamek in his native Poland in September.
The 34-year-old Adamek has moved up to heavyweight after formerly campaigning, like Haye, at cruiserweight and also light-heavyweight.
The bout will take place in one of the newly-built football stadiums being built for Euro 2012 which is being jointly-hosted by Poland and Ukraine.
"Adamek is very experienced, fast and a hard-punching opponent. Whether it is Wladimir or me, we have to be very concentrated during the entire fight," Vladimir Klitschko told their official website.
Adamek has 43 wins from 44 bouts with one defeat, five of his wins coming at heavyweight. He lives and trains in New Jersey in the United States.