Less than a week before a European Council summit, where EU leaders are due to rubber stamp the Prime Minister’s deal, she is braced for fresh attacks from inside and outside her own party.
After a week which saw Cabinet ministers resign over the Brexit deal and the campaign to replace Mrs May broke cover, all eyes will be on Sir Graham Brady, chairman of the backbench 1922 Committee.
Speculation is mounting over whether he has received the 48 letters of no confidence required to challenge her leadership of the Conservative Party.
Mrs May will join Labour leader Jeremy Corbyn in addressing the CBI annual conference in London on Monday.
Her speech is due to address those - thought to include up to five serving ministers - who think changes can be made to her deal before the November 25 summit.
She is expected to say that there is “an intense week of negotiations ahead of us”, adding: “During that time I expect us to hammer out the full and final details of the framework that will underpin our future relationship and I am confident that we can strike a deal at the council that I can take back to the House of Commons.
“The core elements of that deal are already in place. The Withdrawal Agreement has been agreed in full, subject of course to final agreement being reached on the future framework.”
Mrs May’s speech will also seek to set out the positives of her Brexit plan on immigration, creating a meritocratic, egalitarian system that would help Britons get good jobs and training.
She is due to say: “It will no longer be the case that EU nationals, regardless of the skills or experience they have to offer, can jump the queue ahead of engineers from Sydney or software developers from Delhi.
“Instead of a system based on where a person is from, we will have one that is built around the talents and skills a person has to offer.
“Not only will this deliver on the verdict of the referendum, it should lead to greater opportunity for young people in this country to access training and skilled employment.”
CBI president John Allan is expected to call for MPs to back Mrs May’s deal - despite it not being “perfect” - and warn of the consequences of crashing of the EU for businesses and the economy.
“It does open a route to a long-term trade arrangement and unlocks transition - the very least that companies need to prepare for Brexit,” he is expected to tell the conference.
“And most importantly, it avoids the wrecking ball that would be a no-deal departure.”
It was reported on Monday that the EU could extend the transition period by two years in order to allow more time for a trade deal to be negotiated.
According to the Financial Times, the EU’s chief Brexit negotiator, Michel Barnier, told ambassadors the transition could go on until as late as December 2022.
The UK would have to allow the free movement of people throughout and continue making large payments to Brussels, the paper says.
Mrs May, who is due to travel to Brussels this week for talks with EU leaders, used a Sunday interview to hit out at Tory rivals threatening to unseat her as party leader.
She told Sky’s Ridge On Sunday she had not considered quitting, adding: “A change of leadership at this point isn’t going to make the negotiations any easier and it isn’t going to change the parliamentary arithmetic.
“What it will do is bring in a degree of uncertainty. That is uncertainty for people and their jobs.
“What it will do is mean that it is a risk that we delay the negotiations and that is a risk that Brexit gets delayed or frustrated.”
A former Tory chief whip warned MPs against trying to replace Mrs May, saying it could spark comparisons with the end of Margaret Thatcher’s time as PM.
Andrew Mitchell told the Times: “If these letters succeed in triggering a challenge then the party will turn in on itself and that is not a good place for the Conservatives let alone the country.
“It will end making us look like we’re hunting the prime minister down as happened with Margaret Thatcher. It will do the party untold damage in the eyes of the public.”
Reports suggest that MPs opposed to Mrs May could use a Budget bill in Parliament on Monday to cause embarrassment for the Prime Minister.
And former foreign secretary Boris Johnson made yet another colourful attack on her plan.
He used a column in Monday’s Telegraph to describe the agreement as a “585-page fig-leaf (that) does nothing to cover the embarrassment of our total defeat”.
Calling for the scrapping of the Northern Ireland backstop, he added: “We should massively accelerate our preparations to exit on World Trade Organisation terms, with a new secretary of state responsible for all the cross-government work.
“There would, of course, be some disruption in that outcome, but by no means as much as sometimes predicted.
“And it is our failure to make proper preparations that has so gravely weakened our negotiations.”