Former heavyweight titleholder Vitali Klitschko's comeback was put on hold after he suffered a back injury Saturday and underwent immediate arthroscopic surgery in Austria.

Klitschko was training there for a fight in Munich, Germany, on Sept. 22 against American Jameel McCline, which was scheduled to be televised in the United States on Showtime.

"Vitali is doing fine. He was doing his training when his back tightened up," Tom Loeffler of K2 Promotions told ESPN.com. "It needed immediate surgery so they could relieve pressure on the nerve. He is in the hospital right now, but he will be out in three days."

It is the second consecutive time Klitschko, 36, has had to withdraw from a bout because of an injury close to fight time.

Klitschko -- the older brother of heavyweight titleholder Wladimir Klitschko -- vacated his title and retired because of knee and back injuries days before he was to make a mandatory defense against Hasim Rahman in November 2005. After an unsuccessful run for mayor of his native Kiev, Ukraine, Klitschko (35-2, 34 KOs) announced in January that his injuries had healed and that he was planning a comeback.

Loeffler said the new injury was not related to the fighter's previous ailments.

"It was just an unfortunate occurrence, but it's not an uncommon injury," Loeffler said.

Loeffler added that Klitschko's doctor expects a full recovery and for him to be able to resume training in four to six weeks.

"The surgery went well, and Vitali made it clear that he still wants to fight," Loeffler said. "It's disappointing and frustrating, but the main thing is Vitali's health."

Klitschko manager Shelly Finkel was caught off guard by Klitschko's injury, telling ESPN.com, "It's a shock, a total surprise."

The McCline camp was stunned by the news when members found out Sunday evening.

"It's devastating," Mike Borao, McCline's attorney, told ESPN.com. "Jameel just sparred 12 rounds yesterday. He's trained for three months, and five days before we were supposed to go to Germany, this happens? It's a disaster.

"The thing that makes this tough to swallow is that a month ago I heard that Vitali was getting really beat up in sparring and that he was considering pulling out of the fight. I'm not saying the guy is not injured. I'm just saying it's disheartening to hear those things and then this happens. It's so disappointing. It's so hard to take."

Klitschko's trainer, Fritz Sdunek, disputed Borao's assertion about the training camp.

"He had nine weeks of intense preparation. Everything was going fine," Sdunek said in a statement. "He looked better than when he was preparing for the Rahman fight. He was in championship form."

Klitschko-McCline is the third major fight in two weeks to be either postponed or canceled. Fernando Vargas' farewell fight against Ricardo Mayorga, scheduled for Sept. 8 on Showtime PPV, was postponed last month until Nov. 23 because Vargas is ill with anemia. On Friday, a Sept. 15 HBO PPV card headlined by junior lightweight champion Juan Manuel Marquez's first defense against Rocky Juarez was canceled because a cut on Marquez's knuckle developed a severe infection.

The postponements and cancellations have had a heavy impact on Finkel. Besides Klitschko, he also manages Vargas and Juarez.

After being stopped on cuts by Lennox Lewis in a June 2003 title fight, Klitschko went on to win the belt Lewis vacated upon his retirement by stopping Corrie Sanders in the eighth round in April 2004.

Klitschko made one defense, knocking out Britain's Danny Williams in December 2004. Then Klitschko suffered a spate of back and knee injuries that forced him to postpone the fight with Rahman several times until finally retiring.

When Klitschko announced his retirement, the WBC named him "champion emeritus" with the proviso that, should he return, he would automatically be given a mandatory shot at its title, which currently is held by Oleg Maskaev.

Maskaev is due to defend against Samuel Peter on Oct. 6. Klitschko was taking the fight with McCline as a tune-up after such a long layoff. Had he beaten McCline, Klitschko planned to fight the winner of Maskaev-Peter in early 2008.

But with yet another training setback, it appears unlikely that the fight with McCline will be rescheduled. Assuming Klitschko recovers from the latest injury, he probably will take advantage of his mandatory status by forgoing a tune-up and fighting the Maskaev-Peter winner in his first fight back.

Like Klitschko, McCline (38-7-3, 23 KOs) was going to return to the ring coming off an injury. In a Jan. 20 title bout against then-beltholder Nikolai Valuev in Switzerland, McCline lost via freak third-round knockout, falling to the canvas without being hit after tearing ligaments in his left knee. He underwent surgery and hoped a win against Klitschko would propel him into a fourth shot at a heavyweight belt.

ESPN.com