“In spite of Greece having taken more painful adjustment measures than EM peers, public sector debt/GDP (gross domestic product) remains at an excruciating 175 percent, real GDP has failed to recover meaningfully, deposit withdrawals continue and unemployment pressure remains,” Quijano-Evans said in a note on the subject published last week.

Greece was not in a position to reduce its debt/ GDP, he added, and could be reaching the point where its only option was for it to leave the euro zone.

“At a certain stage, an economy cannot take anymore,” he told CNBC Wednesday. “It can’t reach the primary surplus target of about 4.5 percent of GDP, in order to get that debt to GDP ratio down. That’s what the Greek electorate told us some months ago (when it elected anti-austerity party Syriza) and that’s what markets are telling us now.”

His comments come amid deep uncertainty over whether Greece can avoid bankruptcy and default. The country remains embroiled in reforms-for-aid talks with lenders, and a deal– that could release a vital 7.2 billion euros ($8 billion) worth of aid – seems some way off.

European Union Economic Affairs Commissioner, Pierre Moscovici, said Wednesday that an agreement in the next few weeks was “do-able,” but there were still big gaps on pension and labor market reforms, Reuters reported.

In the meantime, Greece is rapidly running out of money and could struggle to pay both its domestic wages and pension bill next month, and debt repayments due to the International Monetary Fund (IMF), and European Central Bank (ECB).

History lessons

History shows us that without a substantial primary surplus or a flexible exchange rate, countries in this situation usually face a default or haircut on their debt, Quijano-Evans said in his report.

Greece’s lenders have so refused to accept a haircut on their debts, however, and are insisting that the country implements reforms before it receives any more financial aid. The country has, after all, already received two bailouts worth a combined 240 billion euros.

Whether Greece remains in the single currency area is now a “political decision,” Quijano-Evans told CNBC, and one that would have to taken in the near-term.

Leaving the euro zone could give Greece the opportunity to devalue an alternative currency, he highlighted – as Argentina did in 2002 when it unpegged its peso from the dollar in a bid to regain competitiveness and stimulate growth.

“The continued dragging in negotiations and the negative spillover into domestic sentiment is additionally hindering any major recovery scenario,” Quijano-Evans said in his report. “Especially as Greece can’t ‘benefit’ from a meaningful weakening of its own currency — aside from the euro drop that we have seen over the past year.”