BERLIN, June 8 - Germany captain Michael Ballack will miss Friday's World Cup opening match against Costa Rica because of a calf injury, coach Juergen Klinsmann told a news conference on Thursday.

"We'll leave him on the sidelines for this game and have him fit for the next one," Klinsmann said.

Ballack, who also missed the final match of the last World Cup because of suspension, suffered a slight strain to his right calf during Germany's 3-0 win over Colombia in a warm-up match on June 2.

The 29-year-old midfielder did not believe it to be serious at the time and alarm bells only started ringing when he was unable to train with the squad on Monday.

He did return to full training on Wednesday but had to drop out after just 30 minutes.

"The important thing now is to look ahead," Klinsmann said. "We want a fully fit Michael Ballack, not a 50 percent player. Fingers crossed he'll be back training soon."

Germany's second Group A game is against Poland in Dortmund on June 14. They wrap up the opening phase with a match against Ecuador in Berlin on June 20.

Klinsmann said Ballack would be replaced in the opening game either by Tim Borowski or the more defensive Sebastian Kehl.