"They are the absolute favourites, there's no question about that," Rehhagel told reporters after a training session north of Porto.
"The Czechs have always been exceptional footballers and they have proved it so far, but we will see whether we can use the few chances that we have to go through."
Relishing their underdog status, the Greeks hope to defend solidly and break open the Czech defence with quick counter-attacks just as they did against champions France in the quarter-final.
Rehhagel will be able to pick from his full 23-man squad for the first time since the start of the three-week tournament as no player is injured or suspended.
His most dependable striker Zisis Vryzas will be eligible to play after missing the quarter-final due to a one-match ban.
"I am happy to be back and at the disposal of the coach for a big game," Vryzas said.
"The teams still left in the tournament are the best ones and the Czechs are probably the best of all at the moment, but we have the right to hope."
Midfielder Stelios Giannakopoulos has returned after missing the last two matches with a leg injury. He was in full training on Monday after more than 10 days out.
