"The consequences would be a disaster for Greece. It would mean at least another five years of recession and unemployment can exceed 40 percent," he said.
The German newspaper Bild reported Wednesday that Samaras also indicated a Greek departure from the eurozone would hurt other economies in the euro currency region.
Samaras is to speak with German Chancellor Angela Merkel this week to request extensions to some of the financial targets laid out in the country's huge international loans.
He also said Greece was not seeking additional funding, only reforms.
"Let me be very clear: We require no additional money. We stand by our commitments and to fulfill all requirements. But we need to boost growth, because that reduces the financial gaps. All we want is a little room to breathe, to get the economy going and to increase government revenues," he said.
"More time does not automatically mean more money."