Greek finance minister Yanis Varoufakis has said he does not believe his country's international partners would allow it to be forced out of the European single currency.
Eleventh-hour bailout negotiations are continuing over the weekend after fears that Greece could default on its massive debts led to falls in stock markets across Europe.
International Monetary Fund negotiators left talks in Brussels on Thursday citing a lack of progress, although Athens officials insist a deal is "closer than ever".
Mr Varoufakis dismissed "silly" demands for widespread cuts to pensions as a "deal-breaker" but said he did not expect the stand-off to end in a Greek exit from the eurozone.
"As a former statistician I would never consent to the notion that there is a zero-probability event," he told the BBC Radio 4 Today programme.
"It is also possible that a comet will hit the planet Earth and your programme will not be playing tomorrow.
"But I do not believe that any sensible European politician will go down that road."
Asked if he believed the IMF and eurozone nations were bluffing, he said: "I hope they are."
He told the programme: "The reason why we are not signing up to what has been offered is because it is yet another version of the failed proposals of the past."
On the pension reform demands, he said: "It is just the kind of proposal that one puts forward if you don't want an agreement.
"This is the kind of proposal that is a deal-breaker and it is just a silly negotiating stance that I think we should simply put aside."
He said the scale of austerity already undertaken by Greece made Chancellor George Osborne's squeeze on the UK's public finances look like "just profligacy galore".
And he sought to play down the level of dissent towards Greece in Germany.
"There are many voices in Germany. The Chancellor (Angela Merkel), I think, is absolutely aware of the issues. I think she does not even begin to contemplate an exit of Greece from the eurozone.
"There are other forces within the government, other forces within Germany, that are divided on this issue.
"What matters, in the context of the European Union, is that we get it together and work towards a sensible solution that is mutually beneficial."