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Germany midfielder Michael Ballack, shown during the football World Cup 2010 qualifying match against Liechtenstein on March 28, 2009, in Leipzig, eastern Germany, is out with an injured ankle. ((RONNY HARTMANN/AFP/Getty Images))

Injured Germany captain Michael Ballack is warning home fans against high World Cup expectations.

Ballack said group rivals Australia, Serbia and Ghana are all "athletic, robust" teams.

"People should know that we could lose against anyone in the group stage," Ballack told Stern weekly in an interview released Wednesday. "Our team will have to play at its limit to beat the big nations in the knockout stage. That was so before my injury and remains so now."

Ballack said Germany, a three-time world champion, could go far in the tournament despite his absence. Ballack will miss the tournament because of an ankle injury.

"Our team has a good mentality. It won't back down. It will go to its limit," Ballack said.

"[Coach] Joachim Loew will draw the maximum from the team, I am sure. In the last two tournaments we were second and third, why can't we do the same now?"