Wladimir Klitschko will defend his WBA, WBO, IBF and IBO heavyweight titles against undefeated Bulgarian Kubrat Pulev in Germany on 6 September.
The Ukrainian last fought in April, beating Australia's Alex Leapai to extend his 10-year winning run.
Pulev, 33, is the IBF's mandatory challenger and is undefeated in 20 fights, with 11 by way of knockout.
Klitschko, 38, said: "He has a sophisticated technique and I won't underestimate him."
The fight will take place at Hamburg's O2 World Arena and Pulev - nicknamed The Cobra - said: "I'm ready to replace Wladimir Klitschko as champion."
However, his Germany-based opponent has been a heavyweight champion since 2006 and has a record of 52 knockouts in 62 wins.
Klitschko, whose last defeat came in April 2004, added: "The Cobra is a challenge for me. I am looking forward to this challenge and can't wait to start my training camp to prepare for the next step of my mission."