The German football federation said Ballack hurt his right calf Friday and did not train that day either, adding that he was receiving treatment at the team hotel.

"We have to see how it develops overnight," Germany coach Joachim Loew said. "They are working around the clock on him."

Loew said he hadn't written Ballack off yet.

"When I saw him this afternoon he was very optimistic despite everything. He was not too down because the doctors say there is still a chance he could play," Loew said. "But of course, it's a disappointment for any player."

Ballack, who has been a key factor in Germany reaching the final, missed out on the 2002 World Cup final because of suspension. The 31-year-old Chelsea midfielder also missed the opening game of the 2006 World Cup because of a similar injury on the same calf.

"It was unthinkable that he would have been able to train today," Loew said.

Ballack, who can both orchestrate and finish off his team's attacks, has scored two goals in five matches at Euro 2008. He hit a fierce free kick against Austria in a first-round match and headed what turned out to be the winning goal in the 3-2 quarterfinal win over Portugal.

Germany flew to the Austrian capital earlier Saturday from its base in southern Switzerland. The team's training session there on Friday was not open to the media and the German federation did not release any information on Ballack's injury until he did not show up for the one practice session before the final match. Saturday's session was open to the media for the first 15 minutes.

"We don't know how he got injured," Loew said. "Sometimes after a game you don't feel it for a day or two. It was inflamed yesterday but no one knows how he got it."

Spain central defender Carles Puyol said he hopes Ballack will take the field at Ernst Happel Stadium.

"He's a very important player," Puyol said. "I don't know if he can play or not. As a footballer, I'd like to see everyone on the field, because its a unique opportunity that you don't know if it will be repeated. It would be too bad if he couldn't be there because of an injury."

Coach Luis Aragones said Ballack's injury wouldn't help Spain because the Germans would find another highly motivated player to replace him.

"Ballack is a great player without doubt," Aragones said. "But I always say it's worse. Whoever comes on for him will run even more."

Ballack's absence would be a severe blow to Germany's hopes of lifting a record fourth European title. Ballack was also looking for his first major title - and he would get if his teammates beat Spain even without him. Spain is also missing a key player, forward David Villa.

Only hours before it acknowledged Ballack's injury, the federation Web site carried an interview with Franz Beckenbauer, Germany's legend and a member of UEFA's executive, who called Ballack the key figure for a German victory over Spain.

"I have a good feeling for Ballack. It's a great chance for him to win his first major title," Beckenbauer said. "That's what he's running for, that's what he's fighting for. He's the absolute leader and he conducts the team on the field. Michael Ballack is the key to victory in the game against Spain."

Ballack's midfield partner, Thomas Hitzlsperger, agreed that their team would be poorer without him.

"He's proven over the years how important he is for the team," Hitzlsperger said. "He's scored so many important goals. He has a big presence on the field, he's a leader, he is someone the younger players look up to."

Loew has revealed little about his possible starting lineup. He had been expected to start with the same lineup that beat Portugal and then Turkey 3-2 in the semifinals, except for midfielder Torsten Frings returning in place of Simon Rolfes. But if Ballack is unable to play, Loew may reshuffle his team in more ways.

"We have to seriously consider what will happen if Ballack will not be able to play," Loew said, adding that he may have to use Tim Borowski or Bastian Schweinsteiger in a different role against Spain.

Loew was still optimistic despite the doubts about Ballack.

"I expect a win. We are going into the game with self-confidence. But Spain has been the most consistent team here, they have had almost no fluctuations in their level," Loew said. "They may be somewhat of a favorite but we are confident and we are going in with a very positive approach