With cash coffers running empty and renewed talk of a Greek eurozone exit without more aid, Samaras is under pressure to convince European leaders that Greece has finally mustered the political courage to fulfill pledges under its latest bailout.
Juncker, the most influential European policymaker to visit Athens since Samaras's conservative-led government took power in June (see background), is expected to bluntly tell Samaras that Greece must carry out promised cuts and that little room for leeway exists.
That message is likely to be hammered home again to the Greek leader when he travels to Berlin on Friday to meet German Chancelor Angela Merkel and to Paris a day later for talks with French President François Hollande.
Days after being elected, Samaras's government promised he would embark on a European tour to seek two more years to hit targets under Greece's €130-billion bailout from the European Union and International Monetary Fund.
But faced with the reality of a messy bankruptcy without further aid, the government has since toned down its rhetoric on the issue and now expects to only broach the idea during talks this week rather than formally requesting it.
"We must first re-establish our relationship with European partners that has been seriously damaged," said a government official, who spoke on condition he not be identified. "This is most crucial. Talking about certain parameters then comes at a second stage."
European paymaster Germany, where patience over Greece has worn thin, has already said it will not soften its demands from the twice-bailed out country.
Wrangling over cuts
Key to restoring credibility will be Greece's attempt to push through €11.5 billion of cuts over the next two years as demanded under the bailout - which Samaras's administration has yet to fully piece together after weeks of wrangling.
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 howls of protest over plans to slash pensions and put civil servants in a so-called labour reserve before laying them off.
"We are trying to find the best possible mix and a fair distribution of pensions. We also have to protect those getting very low pensions," a finance ministry official said. "A second issue we continue to work on is the labour reserve."
Because salary and pension cuts will lead to lower tax revenues, the government will have to find €13.5 billion in nominal savings to achieve its €11.5 billion target, the official said. Parties have identified €10.8 billion in cuts so far.
The measures will be presented for approval to the troika of European Union, European Central Bank and International Monetary Fund lenders due back in Athens early next month for a final verdict on whether to keep money flowing to Greece.
After his election victory in June averted fears of an imminent Greek eurozone exit, Samaras won a positive initial reception from European governments. A Reuters poll last week showed a growing number of economists now believe Greece will remain in the eurozone.
But the debt-stricken 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 European Central Bank and euro zone governments.
Greece blames the slippage on a deeper than expected recession that is now in its fifth year and which Athens has likened to America's "Great Depression". Nearly one out of four Greeks are jobless, and thousands of businesses have shuttered since the sovereign debt crisis exploded in 2009.