Moras is receiving daily physiotherapy and is not training with Greece. Tests Wednesday show he is fully recovered, but he said it is too early to risk playing a World Cup match.
"I don't want to risk it," Moras said. "I want to be fit for Nigeria."
Greece plays South Korea on Saturday and then faces Nigeria on June 17. Its final match is against Group B favorite Argentina on June 22.
There was no immediate word from Greece officials who would replace Moras at the heart of the 2004 European champion's defense.