The European Union and Canada have tried to remain upbeat about the prospects for their trans-Atlantic free trade pact despite a small Belgian region persisting in its refusal to back the deal.
After the setback early on Monday, EU President Donald Tusk and Canadian Prime Minister Justin Trudeau spoke by telephone, with Mr Tusk saying afterwards "there's yet time" to find a compromise solution.
A joint summit for signing the long-delayed trade deal is scheduled for Thursday, offering the two leaders and Belgian officials little time to persuade the Wallonia region to drop its opposition.
Without all Belgian regions supporting the agreement, Belgium cannot sign and the EU needs unanimity from all of its 28 member states.
"We think Thursday's summit still possible," Mr Tusk said in a Twitter message. "We encourage all parties to find a solution."
The EU's inability to sign would be a major embarrassment and undermine the belief that the world's biggest trading bloc is a trustworthy partner as it seeks similar deals with nations like the US and Japan.
Prospects for a signing ceremony on Thursday looked as good as dead on Monday afternoon when Belgian Prime Minister Charles Michel admitted he could not get unanimity in the country's regions and legislatures.
"We have been asked to give a clear answer today," on whether Belgium could sign up as the last of 28 member states," Mr Michel said after meeting with Wallonia leader Paul Magnette. "The clear answer, at this stage, is no."
Even though Mr Michel is eager to sign the deal, Belgium's constitutional set-up means every single region in the country needs to back it, not only the national government.
As a result, opposition from a region of 3.5 million could now stop a deal between more than 500 million EU citizens and 35 million Canadians.
The EU's executive Commission called for patience in an attempt to save the free trade deal and had already dismissed a Monday-night deadline as counter-productive.
Mr Magnette insisted he would agree to nothing under the threat of an ultimatum but remained open to further talks.
The EU Commission, which has negotiated the deal on behalf of the 28 nations, insisted this week's summit was not the final deadline.
"Now, we need patience," EU Commission spokesman Margaritis Schinas said. "The commission traditionally does not set deadlines or ultimatums."
Even if Thursday's summit has to be called off, it could always be rescheduled when Wallonia has signed on to the agreement, Mr Schinas indicated.
Politicians in Wallonia argue the proposed Ceta accord (Comprehensive Economic and Trade Agreement) would undermine labour, the environment and consumer standards.
Proponents say it would yield billions in added trade through tariff cuts and other measures to lower barriers to commerce.