BERLIN - World champion Wladimir Klitschko may suffer from a lack of genuine heavyweight challengers, but he plans to prove his jaw is not made of glass by knocking out France's Jean-Marc Mormeck on Saturday.

World champion Klitschko defends his IBF, IBO, WBO and WBA titles against Mormeck, who stepped up from cruiserweight just over two years ago, in Dusseldorf.

The pair were scheduled to meet last December, but kidney stones forced Klitschko to postpone the fight which will be the 60th of his career and he wants to make Mormeck his 50th knock-out.