Pavel Nedved picked up an injury on his knee during training with the Czech Republic on Thursday after colliding with team-mate David Rozehnal.
Doctors immediatley treated the former European Footballer of the Year, and the medical staff remain confident Nedved will be fit for the opening match against the United States on June 12.
“The knee hurts and that forced him to quit training,” said Czech team physician Dr Petr Krejci.
“We hope that it won’t be anything serious and he will be fit.”
Nedved came out of international retirement to help the Czechs qualify for the World Cup.