Germany captain Michael Ballack missed training on Monday with a calf injury, although team doctors insist it was just a precautionary measure.

The hosts open their World Cup campaign with a Group A game against Costa Rica on Friday, and there are fears that the Chelsea midfielder will miss the clash with the injury, which has dogged him in the past.

However, an upbeat statement from Germany's medical team read: "It was just a precautionary measure as sprint training was on the programme."

The 29-year-old was also forced to miss training for several days at the squad's recent camp in Geneva because of an ankle problem.

He missed the friendly against Luxembourg, although he did play against Japan and Colombia in Germany's final two warm-up games.

The other 22 players all trained on Monday, the first session since the squad reassembled at their Berlin base.