Cut off from markets, Athens is fast running out of cash to pay salaries, service loans and redeem maturing debt. This poses a growing risk that it may default and perhaps have to leave the euro zone.
But Greece has been unable to agree with creditors on what reforms it should implement to release more emergency funding because its left-wing government won election in January on promises of putting an end to austerity.
The €240 billion bailout from euro zone governments and the International Monetary Fund, under which Athens could still get some money, expires at the end of June.
"The financing of the Greek government is not sustainable without a third programme, additional financing," a senior euro zone official said ahead of a meeting of euro zone deputy finance ministers on Wednesday.
That would have to be agreed at the latest in May so euro zone government had time to secure parliamentary approval.
"We are not talking about weeks any more, we are talking about days," the official said.
However, neither the Greek government nor euro zone finance ministers were ready to begin discussing such a new bailout plan for Athens yet, the official said.
Greece did not want to perpetuate the loss of sovereignty over policy-making that bailouts entail and the euro zone wanted to see Athens implement reforms agreed under its existing bailout before starting to discuss any follow-up arrangement.
After three months of talks on reforms that euro zone officials said were "going nowhere", Greek Prime Minister Alexis Tsipras weighed in on Monday (local time), reshuffling his negotiating team and sidelining outspoken Finance Minister Yanis Varoufakis.
"My understanding of what the prime minister said on Monday was precisely that he understands now that he is running out of time. He has decided to step in personally and take control of the discussions," the euro zone official said.
'POLITICAL COST'
Greece plans to present a list of reforms that would satisfy the euro zone at a meeting with representatives of the European Commission, the International Monetary Fund, the European Central Bank and the euro zone bailout fund on Thursday.
But in the creditors' eyes, that will be only the start of a crucial discussion.
"It is probably only next week that we can begin to figure out if there is a tangible chance of success or not. That is not tomorrow, when we see the list of reforms," the official said.
Agreement will be tricky, because the euro zone wants Greece to commit to major policy changes that go against what Tsipras and his Syriza party promised voters, notably on pension and labour market reforms.
"I don't see a possible conclusion if the Greeks don't make a very significant move in one or two or three areas," the official said.
"It could be pensions, it could be the labour market but ... they have to pay the political cost. The Eurogroup wants to see that political cost being paid."
If representatives of the creditors and Greece can agree on such reforms next week, euro zone finance ministers could endorse the deal at their May 11 meeting or at an extraordinary session a few days later if necessary.
"At best, there could be some kind of an interim statement on May 11 and then the completion of the review by the end of May or very early June," the official said.
Once finance ministers declare there is a high probability of agreement and hence of disbursement of the reminder of the existing bailout, the ECB could lift limits on the amount of treasury bills Greek banks can buy. That would immediately ease the government's funding position, giving it some breathing space to negotiate a third bailout.
However, the official cautioned that talks on such a new programme would be even harder than on the current reform plan.
"Everyone knows that any follow-up arrangement will require a substantial amount of fresh money and/or debt reduction, maybe both, or any combination of both," the official said.
"Everything we have discussed so far is very easy in comparison with the next discussion," the official said. (Reporting By Jan Strupczewski; editing by Paul Taylor)
