"The agreement from March 2016 is seriously damaged," said former diplomat Marc Pierini.
A border crisis is brewing in Greece - creating a fresh challenge for Europe when it comes to migration. Brussels has defended Athens' tough stance.
"So this is, of course, a very serious situation and Greece needs all the support from European Union, both from the Commission and from other member states," Ylva Johansson, EU Home Affairs Commissioner told our reporter.
The presidents of the European Commission, European Council and European Parliament will travel to Greece on Tuesday and an extraordinary meeting of Interior Ministers will be called this week to coordinate their response.
But Europe faces another question: on the future of the EU-Turkey deal to stem the flow of migrants.
"I acknowledge that Turkey is in a difficult situation concerning and with regards to the refugees and the migrants but what we see now cannot be an answer or a solution," EU Commission President Ursula von der Leyen told reporters. "Therefore we establish a more and more intensive dialogue with Turkey."
EU foreign ministers are also expected to meet to discuss their response by Friday, but what are the options for Europe? According to former diplomat Marc Pierini, there is no alternative to co-operation with Ankara.
"The agreement from March 2016 is seriously damaged. The Greeks say they don't want to process migrant returns anymore, the Turks say it is still valid, but they really want something else. So the agreement is in serious danger right now. But there is no reason to abandon it, because the fate of the Syrians in Turkey is difficult, and they must be helped."
Although Turkey may have triggered a crisis for domestic gain, Ankara needs to come to the negotiating table, as it cannot afford an economic break with the EU.