Greece would have to introduce another currency if the ‘No’ vote prevails in Sunday's bailout referendum, European Parliament President  Martin Schulz has said.

"Is Greece still in the euro after this referendum? That is certainly the case, but if they say ‘no’ they will have to introduce another currency after the referendum because the euro is not available as a means of payment," Reuters quoted Schulz as saying on Germany's Deutschlandfunk radio on Sunday.

Greeks are voting on Sunday on whether to accept the terms of an international bailout proposal in exchange for economic reforms – and further harsh austerity measures, including tax hikes and cuts in welfare spending.

"The moment someone introduces a new currency, they exit the euro zone,” Schulz said, adding that he had “some hope” Greeks will not reject the bailout-for-reforms proposal.

Schulz’s stark warning is in contrast to the opinion of Greece’s Finance Minister Yanis Varoufakis, who said on Saturday the EU had "no legal grounds" to throw Greece out of the eurozone.

According to Varoufakis, the banks in Greece would reopen on Tuesday following a week-long pause irrespective of the outcome of the vote. His statement came after it emerged that Greek banks are expected to run out of cash by Monday.

In case of a liquidity crunch much will depend on the European Central Bank (ECB), which could decide to extend its emergency liquidity line to Athens or cut it off completely if the ‘No’ vote wins on Sunday, or if Greece defaults on a bond redemption to the ECB due on 20 July.

In another interview published on Sunday Schulz opined that regardless of the results of the Greek referendum the European Union may have to provide emergency loans to cash-strapped Greece to help keep public services running and ensure that the most needy Greeks receive the money they need to survive.

“But this is not a sustainable solution. Only an agreement on reforms and the modernisation of Greece can really help the country and lead it back to more growth,” Schulz said in an interview with German newspaper Welt am Sonntag.

Greeks are voting in a referendum on Sunday to determine whether their country should accept the bailout plan put by the country’s creditors in late June. Greece's overall debt stands at about USD 350 B, of which USD 270 B is owed to the ECB, the International Monetary Fund and some Eurozone member states.