Eurogroup President Jean-Claude Juncker has urged Greece to push through austerity cuts, warning that this was the country's last chance to avert bankruptcy.
Mr Juncker was speaking after meeting Greek Prime Minister Antonis Samaras in Athens.
He said: "I would like to think that as far as the immediate future is concerned the ball is in the Greek corner.
"In fact this is the last chance and Greek citizens have to know this and be fully aware about the fact that the Greek Prime Minister is taking this very seriously."
The Eurogroup chief said he was against a third bailout for Greece, and instead told the country to step up structural reforms and privatisations to drag its economy back from the brink.
"I am not referring to a third Greek program because the troika is in charge of giving an exam to the way the Greek authorities did implement the total second package," he said.
With cash coffers running empty and renewed talk of a Greek eurozone exit without more aid, Mr Samaras will travel to Berlin on Friday to meet German Chancellor Angela Merkel and to Paris a day later for talks with French President Francois Hollande.
Mr Juncker, the most influential European policymaker to visit Athens since the conservative-led government took power on 20 June, acknowledged that Greece was struggling with a "credibility crisis" but reiterated he was against Greece exiting the euro.
His show of support for Greece's government comes as a welcome boost for Mr Samaras, who has begun a charm offensive to convince European leaders he has the will to push through unpopular reforms and deserves more time to do it.
Key to restoring credibility will be Greece's attempt to push through €11.5bn of cuts over the next two years as demanded under the bailout, which Mr Samaras' administration has yet to fully piece together after weeks of wrangling.
"I have explained to Mr Juncker that we have enhanced the privatisation agenda, we are speeding up the necessary structural reforms and that within the next few weeks we shall conclude the €11.7bn budget cuts," the Greek Prime Minister said.
Mr Samaras and his moderate leftist and socialist allies have broadly agreed on the measures, but the government is still struggling to nail down the final cuts amid protests over plans to cut pensions and put civil servants in a labour reserve before laying them off.
The measures will be presented for approval to the troika of officials from the EC, ECB and IMF, who due back in Athens early next month, before a verdict in October on whether to keep money flowing to Greece.
Mr Samaras added: "We are moving decisively towards stabilisation. We have made the commitment of achieving all our targets, and we will honour this, in order to exit this crisis."
The country is hugely off track from targets under its bailout and EU officials expect a further debt restructuring will be likely, with the cost falling on the ECB and eurozone governments.