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. Likewise, the Frenchman is planning to become his country's first world heavyweight champion and to test the strength of the champion's jaw. "Klitschko has something that I want and I need to smash his face in order to get it," said the 39-year-old Mormeck. "I know that he is not happy getting hit. I've already said it and mean it - he has a glass jaw." The 35-year-old world champion has not been beaten since April 2004 when he suffered a fifth-round technical knock-out to Lamon Brewster. Elder brother Vitali, the WBC champion, holds the only other title in the division and Klitschko makes no apologies for the Ukrainians dominating the division. David Haye, from whom Wladimir took the WBA title in Hamburg last July, has branded the champion "a Ukrainian robot" and "a fraud" for taking only fights against perceived less able fighters. But the Briton ignores the point that Klitschko has beaten all obvious challengers and Klitschko refuses to apologise for making his so-called "easy" fights look one-sided. "Maybe it looks simple and one-sided for you guys, but it's demanding a lot of work and concentration and you have to be right on the ball," he said in a press conference. "It doesn't matter what kind of mood you are in, what kind of physical shape you are in, you need to show your best performance on Saturday night. "If our fights were kind of sloppy and we were getting punched in the face, probably that would be exciting for the fans." Klitschko said the brothers will dominate the heavyweight division as long as they keep having fun, but his coach Emmanuel Steward admits the dearth of challengers is a concern. "It is frustrating to me, but there's not a lot we can do about it," said the . "It's unfortunate we don't have any heavyweight challengers in America, and it's not their fault." This will be only Mormeck's fourth heavyweight bout and it will be a considerable upset if he becomes the new world champion. Klitschko has a considerable height advantage and all bar three of Mormeck's 40 fights have been at the lighter weight, including a technical knock-out at the hands of Haye at cruiserweight in 2007. The Frenchman has still enjoyed 22 knock-outs in 36 victories, but has suffered four defeats in his career. "Wladimir is a great boxer in every way, but I've been preparing for years for this moment," said Mormeck, who turns 40 in June.