Wladimir Klitschko is optimistic of overcoming injury to be fit to face David Haye in the summer, but has confirmed elder brother Vitali would step into the ring in his absence.
Question marks have been raised over whether the IBF and WBO holder will shake off an abdominal complaint for the mid-summer fight with WBA champion Haye.
The Ukrainian has twice pulled out of a proposed fight with Dereck Chisora, and speculation is mounting Wladimir's elder brother Vitali will take his place for the June 25/July 2 blockbuster.
Haye has made it clear he will quit boxing when he turns 30 in October, meaning the pressure is on Wladimir to prove his fitness before May when a deadline has been set by the Londoner's camp.
But the 34-year-old claims he will start preparations for his fight against Haye in a couple of weeks.
He told BBC Radio: "I'm still recovering after my injury and in a couple of weeks I will be fit and ready for the preparations."
However, the back-up plan is still on the agenda as he added: "If I can't perform then my brother will step in the ring because he's been in this division a very long time.
"I'm very happy that David Haye eventually signed the contract, it will be the third time we've tried to fight each other.
"He says we have no skills and have fought basically no-one...I think he chose me as the younger brother because he does not think I'm so tough. But he will get knocked out."
Three German football stadiums are leading the race to host the big fight, but other European cities are also believed to be in the running, including Monte Carlo.