Some of Greece's biggest banks may have to shut and merge with their rivals, it has been claimed.
A European official told the Reuters news agency that Greece's four big banks - National Bank of Greece, Eurobank, Piraeus and Alpha Bank - could be reduced to just two.
European leaders are meeting on Sunday in a bid to strike a financial aid deal with Greece.
The Greek Finance Minister has branded European action towards the country "terrorism" in an interview with a Spanish newspaper.
Yanis Varoufakis told El Mundo a trillion euros would be lost if Greece was allowed to crash.
"Why have they forced us to close the banks? To frighten people. And when it's about spreading terror, that is known as terrorism."
Varoufakis said the country's banks would reopen by Tuesday whether a Yes or No vote in Sunday's referendum.
The vote could decide Greece's future as a member of Europe's single currency.
The Greeks have voted to reject the austerity terms demanded by eurozone creditors - so, what happens next?
Greeks have voted to reject the terms of an international bailout, putting it on the brink of a eurozone exit.
Greece's controversial Finance Minister Yanis Varoufakis has released a defiant statement of resignation entitled 'Minister no more!'