The Belgian government said talks to convince the region of Wallonia to give its vital consent to a free trade deal between the European Union and Canada are making progress - two days before the accord is supposed to be signed.
Belgian foreign minister Didier Reynders said negotiators "really are at the final texts", but added that "as you know, there is the last comma, the last word, which are probably the most important".
The trans-Atlantic trade deal needs unanimity among all 28 EU nations, but Belgium is withholding its signature because it requires all of its regions to back it - and Wallonia has resolutely refused to do so.
Wallonia leader Paul Magnette has also refused to negotiate under any deadline pressure.
"We received three ultimatums by now and we are not going to tolerate a fourth one, from anybody," said Mr Magnette. "If there is a fourth one, we will walk away from negotiations."
If there is no quick agreement from Wallonia, it is likely the EU-Canada summit will be scrapped. Prime Minister Justin Trudeau was planning to fly over to Brussels for the official signature.
Politicians in Wallonia, which has a population of 3.6 million compared to over 500 million for the whole EU, argue the proposed accord would undermine labour, the environment and consumer standards.
Proponents say it would yield billions in added trade through customs and tariff cuts and other measures to lower barriers to commerce.
At the same time, the EU says it will keep in place the region's strong safeguards on social, environmental and labour issues.
Mr Magnette said a key hurdle was the issue of "private arbitration" in which multi-nationals can legally challenge governments on policies.
He said Wallonia's insistence on a better deal would bolster EU standards and set a strong precedent for other trade talks between Europe and trading partners like the US or Japan.