Karamanlis has stayed out of the spotlight since then but his name has reappeared in recent days in some Greek media as a potential leader of an interim government in case Prime Minister Alexis Tsipras were to resign if a "yes" vote prevailed.

"Europe is our home, Greece is an undetachable part of Europe," he said in a televised address.

(Reporting by George Georgiopoulos, Writing by Deepa Babington)