World heavyweight champion Wladimir Klitschko has called off the defence of his titles against Frenchman Jean-Marc Mormeck on Saturday.
Klitschko, who holds the IBF, IBO, WBO and WBA belts, was taken to hospital on Friday to have a kidney stone removed.
The 35-year-old initially hoped he would recover in time to face Mormeck in Dusseldorf on 10 December, however his management advised him to pull out.
Klitschko defeated Britain's David Haye on points in July to win the WBA title.
Mormeck, 39, is a former WBC and WBA cruiserweight champion, who was defeated by Haye at that level in 2007. However, he is undefeated since moving to heavyweight in 2009, winning three bouts against Vinny Maddalone, Fres Oquendo and Timur Ibragimov.
Wladimir's older brother Vitali holds the only other major heavyweight belt after defending his WBC title in September against Pole Tomasz Adamek.