The Prime Minister briefed key ministers on negotiations with Brussels on Thursday, amid speculation the Government is moving closer to a deal.
However, Westminster has been rife with speculation of possible resignations if Mrs May gives too much ground to the EU in her attempt to win an agreement.
Work and Pensions Secretary and Leave-backer Esther McVey, who was not at the Downing Street meeting, has already pointedly refused to endorse the Prime Minister's Chequers blueprint for Brexit.
Fellow Brexiters Penny Mordaunt, the international development secretary, and the Leader of the Commons Andrea Leadsom, were also said to harbour deep concerns.
A number of ministers, including Foreign Secretary Jeremy Hunt, Brexit Secretary Dominic Raab, Environment Secretary Michael Gove and International Trade Secretary Liam Fox, were said to have raised concerns during yesterday's meeting which lasted around an hour-and-a-half.
The hardest point of dispute is the central issue of a Northern Ireland "backstop" intended to ensure sure there is no "hard border" with Ireland.
The EU wants Northern Ireland effectively to remain in the single market and the customs union to avoid the need for customs checks until there is a final free trade deal between the UK and the EU.
But Mrs May insists such an arrangement must apply to the whole of the UK to avoid the creation of a "border in the Irish Sea" between Northern Ireland and the rest of the UK.
There are reports that Tory Brexiteers fear she is about to concede to EU demands for an open-ended agreement, whereas she previously promised the border issue would have a deadline.
Without a time limit, critics say Britain could be tied to the EU indefinitely unable to negotiate free trade deals with other countries, and perhaps even remain a "permanent EU colony," in the words of Boris Johnson.
As Mrs May spoke privately to Ministers, Northern Irish DUP leader Arlene Foster warned that ministers could not in "good conscience" accept the proposals currently on the table from the EU.
The DUP's 10 MPs propped up Mrs May's government in the last election and have been swung against her in the Brexit talks before - even suggesting they too would rebel against Chequers in a vote.
"The Prime Minister is a unionist. Many of her cabinet colleagues have assured me of their unionism," said Ms Foster.
"Therefore, they could not in good conscience recommend a deal which places a trade barrier on United Kingdom businesses moving goods from one part of the Kingdom to another."
The DUP's Sammy Wilson, MP for East Antrim, echoed the sentiments as the Belfast Telegraph warned the DUP "Don't trust" Mrs May.
"'Don't take us for granted," he reportedly said. "You break your promises and we then don't feel committed to keeping our side of the bargain'. We will have to consider whether or not they have kept their side of the bargain. If they haven't, there'll be consequences."