Heavyweight world champion Vladimir Klitschko broke off training ahead of next week's title defence against French challenger Jean-Marc Mormeck to have a kidney stone removed, his management said on Saturday, adding the bout was still going ahead.
"Vladimir is now receiving medical treatment," the Ukrainian's management official Klaus-Peter Dittrich told Reuters.
"The planning and preparation for the fight are going ahead as planned."
Klitschko, who holds the IBF, IBO, WBO and WBA versions of the title, was taken to hospital in Austria late on Friday, where he has set up his training camp ahead of the bout in Duesseldorf on 10 December.
The 35-year-old will be looking to clinch his 50th knockout from 60 professional bouts when he takes on the former cruiserweight world champion Mormeck.
Klitschko's older brother, Vitali, holds the only other major heavyweight belt after defending his WBC title in September against Pole Tomasz Adamek.