Heavyweight champion Wladimir Klitschko suffered a torn abdominal muscle on Wednesday, forcing him withdraw from his title defense against England's Dereck Chisora four days before the fight.
Klitschko was due to make his 10th title defense against the little-known Chisora at the SAP Arena in Mannheim, Germany, on Saturday -- a fight due to be carried by ESPN in the United States.
However, during his final workout hitting the pads with trainer Emanuel Steward, Klitschko suffered the injury, manager Bernd Boente told ESPN.com.
"He was hitting the mitts and it just happened," Boente said. "The fight is canceled. The pain is extreme. He couldn't even sit in the car on the way to the hospital."
Chisora, in an interview with BBC radio, cast doubt on the withdrawal.
"When we saw him ... everything was good," Chisora said. "I just think he didn't want it."
Klitschko (55-3, 49 KOs) had gone through a public workout earlier in the day, although they are light and just for show. However, Boente said a couple of hours later, he was working with Steward for real when he felt a sudden pain.
Boente said Klitschko, 34, underwent a CT scan and was diagnosed with a 2-inch tear on the left side of his abdominal muscle near the bottom of his rib cage.
"The doctor said he needs four to six weeks to heal," Boente said. "Wladimir has never had to cancel a fight before. He is totally upset. He had a great training camp in the Austrian mountains. He was in fantastic shape and he's very, very upset and very sad. And not only for him but for all the people who bought tickets to the sold-out arena. We were all looking forward to the fight. We are sorry for the fans and for our TV partners. What can you do?"
"The abdominal muscle is injured and therefore Wladimir Klitschko will not be able to fight on Saturday," Dr. Sven Roessing, an orthopedic specialist at University Hospital in Mannheim, said in a statement released by Klitschko's K2 Promotions.
Boente said the entire card, which also was to feature cruiserweight contender Ola Afolabi and middleweight contender Andy Lee, has been called off.
Boente said he was not sure if the fight with Chisora (14-0, 9 KOs) would be rescheduled.
"We don't know. This just happened," Boente said. "We have to check all the options."
Chisora told the BBC he is confident the fight will happen. "He offered the fight and he has to fight me," he said.
Dan Rafael is the boxing writer for ESPN.com. Information from The Associated Press was used in this report.