Eastern European leaders have been Greece's most vocal critics. On Sunday Robert Fico, the prime minister of Slovakia, said "it is high time" to evict Greece from Schengen, adding that all member states were privately in agreement on the issue. "We cannot tolerate one of the member countries openly refusing to fulfil its obligations to protect the Schengen borders," said Mr Fico. "In such a situation, the Schengen area is useless."
Berlin has so far resisted calling for Greece to be suspended or expelled. But behind the scenes, frustrations are growing in Austria and Germany, who have both considered sending special envoys to Greece to support the migration efforts, according to one official familiar with the plans.
"The red line for the Germans was not allowing Frontex to come in and help them," said one EU ambassador in Brussels. "The Germans are furious and that's why people are talking about pushing Greece out."
Two EU ambassadors said debates over Greece were becoming increasingly heated, with Luxembourg, which holds the rotating chair of the EU council of member states, warning Greece that "other measures" may be taken unless it makes good on its promises.
Some Greek analysts suspect Athen's foot-dragging on border controls may be partly about trying to win concessions on implementation of its third bailout: softer terms on tough measures such as pension cuts and farmers' taxes, for example, and postponements of unpopular structural reforms.
Aris Hatzis, an Athens university professor and political commentator, says: "Tsipras saw the refugee issue as a bargaining chip but it's going to backfire disastrously if the threat of Schengen suspension becomes a public issue."
The Commission will deliver an oral update on Greece's situation to a meeting of EU home affairs ministers on Friday, followed by a written assessment to a summit of EU leaders in mid-December.
If serious shortcomings are still evident, Athens has been warned that EU leaders may request the commission start suspension proceedings, triggering a review of Greece's borders that can take three months.