Juncker became the most senior European leader to visit Athens since a new conservative-led government took power in June, promising to fulfil austerity pledges Greece made to receive a bailout, but to seek more time to reach the targets.
Prime Minister Antonis Samaras's plea for "air to breathe" has been met with hostility in the Netherlands and European paymaster Germany. Juncker said a decision to grant more time would depend on the findings of a review by EU and IMF lenders on the country's progress in fulfilling its pledges.
He accompanied that with a warning to Greece to shore up its dire finances, saying the country's next tranche of aid would depend on it producing a credible strategy for austerity cuts.
"As far as the immediate future is concerned the ball is in the Greek court," Juncker said. "In fact this is the last chance and Greek citizens have to know this."
Juncker acknowledged that Greece was struggling with a "credibility crisis" but reiterated he was against Greece exiting the euro which he said would be of no help to Greece and "entail major risks for the whole euro area." He said he was against a third bailout for Greece, and instead urged Athens to step up structural reforms and privatisations to drag its economy back from the brink.
The Eurogroup’s president show of support for Greece's conservative-led government comes as a welcome boost for Samaras, who has begun a charm offensive to convince European leaders he has the will to ram through unpopular reforms and deserves more time to do it.
"All we want is a bit of 'air to breathe' to get the economy running and to increase state income. More time does not automatically mean more money," Samaras told Germany's mass-market Bild newspaper before the talks with Juncker.
"Let me be very explicit: we demand no additional money. We stand by our commitments and by fulfilling all our requirements."
That failed to impress the Dutch finance minister, whose country has been a vocal critic of Greece's slow pace of reform.
"If it concerns delaying reforms and budget cuts, then it is not a good idea," Jan Kees de Jager told reporters.
No Greek exit
Appointed in June after two tumultuous parliamentary elections (see background), Samaras has been juggling opposing demands from voters at home fed up with austerity and irate policymakers abroad demanding more painful cuts from Greece.
With cash coffers running empty and renewed talk of a Greek eurozone exit without more aid, Samaras travels to Berlin on Friday to meet German Chancellor Angela Merkel and to Paris a day later for talks with French President François Hollande.
Initially vocal about demanding more time from lenders, Samaras's government has toned down its rhetoric on the issue in recent weeks and now expects merely to broach the idea during talks this week rather than formally request it.
Merkel has already said she and Samaras will not make any decisions during their talks, adding she too would wait for the lenders' report on Greek progress in meeting targets. That report is not expected until late September.