The PM is in Brussels where she has been lobbying European chiefs to change the hated backstop which looks set to doom the deal.
But the leaders ended up taking a harder line than before after hearing from Mrs May last night.
They are apparently playing hardball because they believe that if the deal is vetoed by Parliament, a second referendum is more likely than No Deal.
Tony Blair has been egging the EU on today, telling them they should prepare for Brexit to be delayed and then cancelled.
This morning the PM was seen snapping at top Eurocrat Jean-Claude Juncker after he dismissed her pleas.
Mrs May flew to Brussels yesterday for the European Council summit after scraping through a vote of confidence from her own MPs.
She is seeking changes to the backstop – designed to keep the Irish border open – to ensure Britain doesn't end up trapped in the EU customs union.
A draft version of the summit's conclusions provided a glimmer of hope for the PM, stating that the backstop "does not represent a desirable outcome" for the EU.
It added: "The Union stands ready to examine whether any further assurance can be provided."
But after Mrs May made her pitch to the other 27 leaders, they changed the text to remove both of the helpful statements.
Instead, the final version calls on EU states to step up No Deal planning.
Belgian leader Charles Michel said this morning: "We have to tell the truth – my impression is that we have to speed up preparations for a No Deal."
The PM has warned Brussels that if they don't give ground, the Commons will trash her deal and Britain will crash out without any deal in March.
But several senior European politicians have sugggested they don't believe her – because it's more likely the UK will hold a second referendum and cancal Brexit altogether.
Yesterday Ireland's Leo Varadkar said: “It is within the gift of the UK Government and UK Parliament to take the threat of No Deal off the table by revoking Article 50 or seeking an extension of Article 50."
And this morning he added that he was "very satisfied" with the EU's decision to play hardball.
Today Mrs May holds a one-on-one meeting with Emmanuel Macron to try and convince him to budge.
After last night's talks, European Commission boss Mr Juncker said: "We don't want the UK to think there can be any form of renegotiation, that is crystal clear.
"We can add clarifications but no real changes. There will be no legally binding obligations imposed on the withdrawal treaty.
"Our UK friends need to say what they want, instead of asking us to say what we want."
Danish PM Lars Løkke Rasmussen claimed rebellious British MPs need to "get some homework done" before they oppose the current deal.