The 30-year-old striker is being assessed by the national team doctor amid fears that he has ruptured a groin muscle, possibly ruling him out of the tournament in Poland & Ukraine
The ex-Liverpool man is a key part of Michal Bilek's squad and was in line to start their opening game against Russia on 8 June in Wroclaw.
However, it is thought that striker, who has scored 41 goals in his international career, picked up a potentially tournament-ending injury in training.
Team doctor, Petr Krejci, told Czech website isport.cz: "We do not know if it's just a muscle contracture, which would be quite favorable, or that there was a rupture.
"If he will be able to play against Russia we still can not tell."
If the Galatasaray hitman, who is the second highest Czech Republic goalscorer in the country's history behind Jan Koller, is unfit, the team's fortunes may fall to the feet of CSKA Moscow starlet, Tomas Necid.