Wladimir Klitschko to defend belts against Kubrat Pulev in September

Wladimir Klitschko is looking forward the "challenge" of Kubrat Pulev

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."