Donald Tusk today hinted at fears that Theresa May will be ousted as he paved the way for an EU summit to sign off the Brexit deal.
The EU council chief said leaders will gather to approve the long-awaited text on November 25 - but raised eyebrows by adding the caveat 'if nothing extraordinary happens'.
The remark came amid huge pressure on the PM from Tory MPs, the DUP and Labour over the package thrashed out with Brussels.
Mrs May is facing the threat of Brexiteers triggering a no-confidence vote within days.
Even if she survives that there is a huge challenge looming in getting the deal through Parliament.
Speaking at a press conference alongside Michel Barnier in Brussels today, Mr Tusk said ambassadors from the EU states would meet by the end of the week to consider the situation.
'Then if nothing extraordinary happens, we will hold a European Council meeting in order to finalise and formalise the Brexit agreement.
'It will take place on Sunday the 25th of November at 9.30am,'
Mr Tusk paid tribute to the work of Mr Barnier and his team, who he said had 'ensured the limitation of the damage caused by Brexit'.
He said he wanted to make the Brexit process 'as painless as possible'.
In a moment of high drama last night, PM emerged from a marathon five-hour Cabinet meeting to declare she believes with her 'head and heart' her deal 'is firmly in the national interest' - and her ministers had backed her.
Mr Barnier told a press conference in Brussels shortly afterwards: 'This agreement is a decisive and crucial step in concluding these negotiations.'
He added: 'We have reached a crucial stage, an important moment in this extraordinary negotiation, which we entered into at the request of the United Kingdom.
'There is still a lot of work...the path is still long and may well be difficult to guarantee an orderly withdrawal beyond the ordinary withdrawal, beyond the ordinary separation, to build something - to build an ambitious and sustainable partnership with the United Kingdom.
'There is still work to be done.'
The EU negotiator paid paid tribute to the hard work of the negotiating teams and said the deal protects the rights of the millions of EU nationals in Britain and the vice versa.
Mr Barnier said the deal 'is the result of very intense negotiations started 17 months ago. I would like to thank both teams...for their hard work.
'It has been an honour and privilege to have been part of quite an exceptional team.'
The EU negotiator said he never saw Britain and Brussels and enemies and wants the UK to be the bloc's 'friend and ally'.
Mr Barnier said the EU has finally found a way, with Britain, to maintain a soft Irish border - the thorniest issue in the Brexit talks which had threatened to derail the negotiations.
He said Britain could extend the transition if no agreement has been done, or decide to switch to the backstop set out in today's deal.
But he admitted that Northern Ireland will be subject to more single market rules than the rest of the UK - a move which will spark fury among the DUP who are propping the Tories up in No10.
Mr Barnier added: 'In the backstop scenario we agree to create the EU - UK single customs territory. Northern Ireland will remain in this same customs territory.
'In addition, Northern Ireland will remain aligned to those rules in the single market which avoids a hard border. This concerns agricultural goods as well as all products.'
It comes after Mrs May emerged from hours of bitter wrangling in Cabinet tonight to hail her Brexit deal, which she said is 'firmly in the national interest'.
After nearly five hours of behind-closed doors discussions, the PM declared that she will press ahead with her controversial plan.
Speaking on the steps of Downing Street, she said the debate had been 'long and impassioned'.
'The choices before us were difficult... but the collective decision of Cabinet was that the government should agree the document,' Mrs May said.
'I know that there will be difficult days ahead. But the choice was this deal... or going back to square one.'
'I firmly believe with my head and my heart that this is a decision that is in the best interest of the United Kingdom.'
So far Mrs May appears to have avoided resignations by senior ministers over the draft blueprint thrashed out with Brussels.
Aid Secretary Penny Mordaunt, among those closest to the edge, is believed to have demanded assurances from the premier on key points.
Senior MEP Guy Verhofstadt, the European Parliament's Brexit Coordinator, hailed the positive progress made in the Brexit talks today.
He said: 'We welcome the positive progress made in the negotiations by Michel Barnier and his team, who have consistently fought for the interests of the European Union.
'We look forward to being fully apprised of the details of the withdrawal agreement tomorrow morning by Michel Barnier, the EU's chief negotiator.
'It is encouraging to see that we are moving towards a fair deal that should ensure an orderly withdrawal, including a backstop guaranteeing that there will be no hardening of the Northern Irish/Irish border and that the Good Friday Agreement will be safeguarded.
'This deal is a milestone towards a credible and sustainable future relationship between the EU and the UK
'It is now up to elected parliamentarians on both sides of the Channel to do their work and scrutinise the proposed deal, including the political declaration and the framework for future relationship.
'Throughout the Article 50 negotiations, we have fought for a people – first Brexit, and we are committed to forensically monitor closely the implementation of the citizen's rights parts of the agreement.
'The European Parliament will have the final say, along with the UK Parliament, on the deal.'
This article has been adapted from its original source.
© Associated Newspapers Ltd.