Greece could seek legal action to stop the country being forced out of the eurozone if it fails to seal a debt deal, The Daily Telegraph reported on Monday.
"The Greek government will make use of all our legal rights," the British newspaper quoted Greek Finance Minister Yanis Varoufakis as saying."We are taking advice and will certainly consider an injunction at the European Court of Justice. The EU treaties make no provision for (a) euro exit and we refuse to accept it. Our membership is not negotiable."
No country has ever withdrawn from the common currency, but the prospect of Greece crashing out of the euro has grown after its long-running debt crisis took a dramatic turn over the weekend.
Talks between Greece and its international creditors collapsed after Athens rejected demands for austerity measures in return for cash and announced it would hold a referendum on the deal on Sunday.
European leaders have urged Greek voters to back the hotly disputed terms, warning that rejecting the proposals would be a vote against staying in the eurozone.
Greek Prime Minister Alexis Tsipras has left open the door for further talks, while making clear that Greece cannot make a 1.5 billion euro ($2.3 billion) payment due to the International Monetary Fund on Tuesday, when its international bailout programme expires.
The Greek government imposed capital controls and ordered banks and the stock exchange to close for a week, with long queues forming at the ATMs in the country.
EU leaders have indicated they are still open to an agreement to avoid a Greek exit, which would leave a permanent scar on the 28-member bloc.