WBC world heavyweight champion Vitali Klitschko will defend his title against Poland's Albert Sosnowski in Schalke's soccer stadium on May 29, the Ukrainian said.
The 38-year-old Klitschko, whose brother Vladimir will defend his WBO, IBF and IBO titles against Eddie Chambers on March 20, said Sosnowski, 31, would be a tough rival.
"He is experienced, he is fast and he is a tough boxer who will try everything to take my belt. But I will not let it happen," Klitschko said in a statement.
"I promise all fans an unforgettable evening."
Sosnowski, the European Boxing Union heavyweight champion with 45 wins, two defeats and a draw, was due to defend his European title against Audley Harrison in London in April but cancelled to fight Klitschko.
"This is a dream come true," he said.
"I was already training for the Harrison fight when I suddenly get the chance of a lifetime. Vitali is way past his peak," he said.