World Boxing Council heavyweight champion Vitali Klitschko has retired because of a knee injury.
In a statement Wednesday, the Ukrainian pulled out of Saturday's title defense against American Hasim Rahman in Las Vegas.
Klitschko had surgery Tuesday after tearing right knee ligaments during training last week. The WBC told Klitschko he had 90 days to make a mandatory title defense before the title would be awarded to Rahman. But the injury needs six months to heal properly.
In the statement, Klitschko said retiring was a difficult decision, but that he wanted to end his career on top. He also said he had spent more time recently fighting injuries than facing rivals in the ring.