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.
Wladimir's manager Bernd Bonte said: "He is sad but he feels extreme pain."
Bonte added there were provisional plans to stage the fight on 3 March 2012, the nominal date for Klitschko to fight a mandatory challenger under IBF rules.
WLADIMIR KLITSCHKO'S RECENT FIGHTS
- 2 July 2011 - beat David Haye in Hamburg (unanimous points decision)
- 11 September 2010 - beat Samuel Peter in Frankfurt (10th round stoppage)
- 20 March 2010 - beat Eddie Chambers in Dusseldorf (12th round knock-out)
"We hope to know in two or three days. Mormeck is also ready to accept it."
After undergoing the operation on Saturday Klitschko spent the day in hospital with a high temperature and inflammation.
"Wladimir shouldn't fight any time soon," German urologist Peter Albertz said during the press conference.
"Anyone who sustains two surgeries in a span of less than 24 hours needs considerable time to rest.
"He is very weak after two surgeries and it makes no sense to have a fight now."
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.