Heavyweight titleholder Ruslan Chagaev, due to defend his belt in a rematch with former titlist Nikolai Valuev, withdrew from their May 31 fight in Germany on Tuesday, claiming illness.
The fight has been rescheduled for July 5 in Hannover, Germany.
"Ruslan Chagaev suffers from a protracted virus infection," said his physician, Dr. Michael Ehnert, in a statement released by promoter Universum Box-Promotion. "In medical terms it's a viral laryngitis and pharyngitis. For non-doctors, it's a highly feverish viral infection of the upper respiratory tract with heavy symptoms. The medical treatment makes it absolutely necessary that he stop training."
According to Universum, Michael Timm, Chagaev's trainer, was forced to miss the successful cruiserweight title defense of stablemate First Arslan last Saturday with similar symptoms.
It is the second time that Chagaev has pulled out of a defense because of illness. He was scheduled for a unification fight against then-titleholder Sultan Ibragimov eight months ago but withdrew because of an undisclosed medical issue described by Universum at the time as "an acute inflammation of the body." Numerous sources reported that he was suffering from hepatitis B.
Chagaev (24-0-1, 17 KOs), an Uzbekistan native based in Germany, returned from his illness to defend the title with a lopsided decision against England's Matt Skelton on Jan. 19.
Chagaev, 29, claimed his title with a majority decision against the 7-foot, 320-pound Valuev, 34, in April 2007.
Valuev (48-1, 34 KOs), of Russia, earned another shot at Chagaev with a shutout victory against former beltholder Sergei Liakhovich on Feb. 16 in an official WBA elimination match.
Dan Rafael covers boxing for ESPN.com. The Associated Press contributed to this report.