Antonis Samaras said proposals by the radical left party to withdraw from international bailout commitments would lead to “certain and immediate” catastrophe.
Mr Samaras, who came first in national elections, is to meet Alexis Tsipras as part of the radical Left leader’s efforts to form a coalition government after Sunday’s elections produced a deadlocked result. If no solution can be found, new elections will have to be held.
Mr Tsipras has said Greece should pull out of the bailout commitments. Mr Samaras says that would mean leaving the euro.
Mr Samaras stressed it was imperative for the country to remain in the euro. Although he has called for the bailout terms to be renegotiated, he said pulling out completely would be disastrous.
“Denouncing the agreement, that (Tsipras) proposes, will lead to immediate internal collapse and international bankruptcy, with the inevitable exit from Europe,” he said. “The agreed amendment of the loan deal is one thing, it is a completely different thing to unilaterally denounce it.”
He added: “If he does not do this, it means that he is trying to build a broad anti-European front and to take us to elections again. The Greek people have not given a mandate to destroy the country,” Mr Samaras said.
Mr Samaras controls 108 of parliament’s 300 seats, Mr Tsipras, whose party won 52 seats, cannot form a government without his support.
Greece has depended on rescue loans from its European partners and the International Monetary Fund since May 2010, after decades of profligate state spending and false accounting priced it out of money-lending markets.
To secure the bailouts, Athens took a hatchet to pensions, salaries, health care and pretty much everything else, while repeatedly raising taxes.
But more than two years of austerity have left the economy deep in recession and unemployment at 21 per cent.