A Brexit deal is not expected to be struck tonight ahead of the crunch EU council meeting in the morning, according to government sources.
The UK and EU had hoped to agree on a revised Brexit deal before Thursday morning so EU leaders could adopt the deal at the meeting.
But government sources told both Sky News and the BBC that a deal would not be agreed tonight as officials continue to work on technical details in Brussels.
It comes as Boris Johnson has been working to persuade both Tory Brexiteers and the DUP to back his revised plan for Northern Ireland.
The EU's chief Brexit negotiator Michel Barnier has also been briefing ambassadors on the state of talks this evening.
The BBC's Laura Kuenssberg said it was not now clear whether there would be a deal at all this week amid reports that VAT remains a sticking point in the agreement negotiations.
If a deal is agreed by both the government and the EU, Mr Johnson will need the support of 320 MPs to get it through the Commons.
Earlier Mr Johnson's Cabinet threw its “full support” behind the PM to secure a new Brexit deal amid last-gasp talks with the EU.
Ministers were pictured smiling as they left Downing Street after a Cabinet meeting on Wednesday afternoon.
Mr Johnson's spokesman said: "The Prime Minister gave an update to Cabinet on the progress in the ongoing Brexit talks.
"He said there was a chance of securing a good deal but we are not there yet and there remain outstanding issues.
"Following a positive discussion, Cabinet gave the PM its full support in the Government's continuing efforts to secure a deal ahead of European Council."
Tory MP Steve Baker, chairman of the pro-Brexit European Research Group of MPs, whose support in Parliament could also be vital, spoke to reporters after a meeting in Downing Street on Wednesday evening.
Mr Baker said that his colleagues will be looking at any deal “with a view to supporting it”.
He said: “We have made great progress in our discussions with Number 10."
He added: “Really at this point, it just remains to wish the Prime Minister every possible success as he goes to negotiate for our country."
Asked if he would back a deal, he said: “I know everybody is desperate for us to say whether we can vote for it, but until we can see it, we can’t say.
“We really must see the text in time to read it in order to vote on Saturday.
However, the Leader of the Independent Group for Change and former Conservative Anna Soubry has described the amount of time MPs would have to scrutinise Boris Johnson’s prospective deal on Saturday as “plain wrong”.
“It is increasingly clear Johnson’s ‘new’ deal is worse than May’s,” she tweeted.
“Parliament will get 5 hours debate on Saturday without any independent assessments, analysis or select committee scrutiny of the most important set of decisions we will make in generations.
“That’s plain wrong.”
Efforts to stop the Prime Minister even putting his deal before Parliament are now being made as anti-Brexit campaigner Jo Maugham QC said he plans to launch a legal action.
He tweeted: “I intend to lodge an immediate petition for an injunction in the Court of Session preventing the Government from placing the Withdrawal Agreement before Parliament for approval.
“We expect that petition to be lodged tomorrow and to be heard on Friday.”
