NEW YORK (TheStreet) -- As meetings between Greece and its creditors drag on,  media reports say that the IMF has refused some of Greece's debt proposals.

Greek Prime Minister Alexis Tsipras said on Twitter (TWTR) - Get Report that "the repeated rejection of equivalent measures by certain institutions never occurred before -- neither in Ireland nor Portugal."

The latest setback is "very significant," according to Markus Will, an economics professor at the University of St. Gallen. "The deadline is too tight for any further new proposal," he added.

Throughout the past week, there has seemed to be alternately progress and roadblocks in the ongoing conversations between Greek and European leaders. Talks continue today as next week's June 30 IMF repayment deadline approaches.

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"I think the likelihood of a deal is still there," said Will. "It's probably even higher than 50%, but it's certainly not 100%."

Will pointed out another big issue: even if an agreement is hammered out getting Greek lawmakers to approve it won't be easy. "If the austerity program is tight, Mr. Tsipras will have problems getting that through his parliament, because he was elected with the promise to end the suffering situation of the Greek population." 

When asked if the Greek negotiations in the end will make Europe strong or weaker, Will responded that "if the eurozone and European Union stick to its rules and with that, obviously allow some social easing for pensioners and younger people in Greece, they will regain or keep the trust which markets and other political leaders do have of the European Union. On the other hand, if that makes the deal fail, we would at most run into at significant political problems in the European Union, because Greece is, in geopolitical terms, a very important country, being a member of NATO."