Moras has failed to recover from a right ankle injury sustained in training and will now look to be fit for Greece's second Group B game, against Nigeria, in Bloemfontein on 17 June.
"I'm not ready," he said. "There's no need to take a risk. "It would be too big a risk to take in such a crucial match. I'll now try to get fit for the second game against Nigeria."
Greece play the Korean Republic in Port Elizabeth on Saturday and, after the Nigeria game, round off their Group B campaign against Argentina on 22 June in Polokwane.