MANNHEIM (Germany) (AFP) - Ukrainian boxer Vladimir Klitschko has pulled out of his heavyweight world title defence against British challenger Dereck Chisora citing an injury. Klitschko, 39, holder of three world heavyweight crowns, announced on his website Thursday that he had injured a stomach muscle in training the day before and would be unable to box in Mannheim, Germany, on Saturday. It was the first time the Ukranian, who holds the WBO, IBF and IBO heavyweight titles, had been forced to miss a title bout through injury. Chisora, 26, who turned professional in 2007, has won all his 14 bouts and was hoping to become Britains second world titleholder after David Haye, who holds the WBA belt.