Wladimir Klitschko will defend his WBA, IBF, WBO and IBO heavyweight titles against Australian challenger Alex Leapai in Oberhausen, Germany, on April 26.
The bout will be the Ukrainian fighter's 25th world championship fight and pits him against the six-foot Leapai, who defeated the previously unbeaten Denis Boytsov in November to become the WBO's mandatory challenger.
"I am wary, but I will prepare myself as well as I can and I'm looking forward to a great challenge," said Klitschko, who will turn 38 in March and has recently spent much of his time alongside his brother in the protests against Ukrainian leader Viktor Yanukovych in the capital Kiev.
Leapai, 34, who was born in Samoa, has a 30-4-3 record with 24 knockouts since turning professional in 2004.
He said: ""Everyone talks to me about Wladimir's 61 victories and how great he is, but all I'm thinking about are his three defeats against opponents who can't strike as hard as I can.
"I'll beat Wladimir and it won't even be my toughest fight."
Klitschko comfortably defeated Alexander Povetkin of Russia in Moscow last October in his latest defence, and has a record of 61-3 with 52 KOs.
Klitschko's older brother Vitali, the former WBC champion, stepped back from boxing to concentrate on politics in their native Ukraine.