Koller was carried off just before half-time against USA

Koller had hoped to be back in training by Friday after scans revealed the hamstring injury sustained in the 3-0 defeat of the USA was not too serious.

But Czech doctor Jiri Foucek said the recovery period "could be anything between 10 days and six weeks".

Foucek added: "We hope that Jan would be able to play in a quarter-final."

Koller was stretchered off just before half-time in Monday's group opener and had initially been expected to miss the rest of the tournament.

"When I first felt the pain I thought 'everything is over for me'," revealed the 33-year-old.

"But the scan says nothing is torn, which I am so happy about."

Koller scored the opening goal in his side's impressive victory over the US.

He added: "I am not sure if I will make it for the next game but at least after three or four days I should be able to train again."

Baros has also had injury problems

Koller's optimism was in sharp contrast to the gloom in the Czech camp immediately after the match, and if the doctor's report is anything to go by, it may be misplaced.

"The injury is really, really serious and it makes me very sad," said coach Karel Bruckner.

Koller had only recently recovered from a cruciate ligament injury that forced him to miss most of the season.

The Czech Republic's other first-choice striker, Milan Baros, did not play against the Americans because of a foot injury.

The Czechs take on Ghana in Cologne on Saturday in their next Group E match.