Vitali Klitschko has 41 career wins
David Haye's hopes of unifying the world heavyweight title have receded further after Vitali Klitschko announced a fight on 19 March.
The Ukrainian will defend his WBC crown against unbeaten former Olympic champion Odlanier Solis in Cologne.
Wladimir Klitschko, the IBF and WBO champion, has already agreed to fight Britain's Dereck Chisora on 30 April.
It now seems unlikely WBA title-holder Haye will face both brothers before he retires from boxing in October.
Haye, who has repeatedly vowed to hang up his gloves before his 31st birthday, said last week he had all but given up on fighting Wladimir Klitschko.
A date of 2 July had been suggested for their clash, but following the announcement of Wladimir's fight with Chisora, Haye was pessimistic about the chances of that fight taking place.
Haye told BBC Radio 5 live last week: "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 announcement of Vitali Klitschko's title fight with Solis leaves only a small window of opportunity for Haye to fight the brothers before October.
If he fails to fight either of the Klitschko brothers, he could face a mandatory challenger or risk being stripped of his WBA title.
"Solis is an experienced, quick and uncomfortable fighter," said Vitali, 39, whose last fight was a win over Shannon Briggs in October. "I will not underestimate him."
The 30-year-old Cuban, an Olympic gold-medallist in 2004, lined up a shot at the title with a win over Ray Austin last month.
"Vitali has been choosing weak opponents for years," said Solis, who has won all of his 17 pro fights. "But that is finished now. I will beat him, take his belts and leave Cologne as champion."