"We don't have the choice of players we had in the 1990 World Cup or in the 1996 European Championship," Ballack said in an interview with the German Berliner Tagesspiegel.

"As a result the team makes mistakes and that's why there is a little uncertainty ahead of the tournament."

The Germans head into the World Cup with a less-than-stable record.

While they beat Columbia 3-0 in their final warm-up match, they drew 2-2 with Japan and were beaten 4-1 by Italy.

"The results and performance in the run-up to the World Cup show that this team is not so stable," the new Chelsea signing said.

West Germany won the 1990 World Cup with stars such as Lothar Matthaus, Thomas Hassler and Rudi Voller.

They were also crowned European champions in 1996 with Matthias Sammer, Andreas Moller and Jurgen Klinsmann leading the team.

Klinsmann is now coaching the team and has said anything less than winning the trophy would be a failure.

While the 29-year-old skipper agrees with Klinsmann's objective he admits the team is flawed.

"We need to be clear that we can't all have an offensive mindset," the former Bayern Munich midfielder said.

"We want to base our game on attack and get forward quickly but sometimes we go forward too quickly and lose the ball.

"But there are still a lot of things to encourage us and we can certainly do it (win the World Cup)," a hopeful Ballack said.

Germany and Costa Rica are joined in Group A by Ecuador and Poland.