Gyimah, a former aide to prime minister David Cameron praised May's "grit and determination", but his resignation highlights the daunting task of getting the deal through parliament, with both Remainers and Brexiteers in her own party vowing to vote it down on December 11. The big season finale of the Game of Votes.
May's government is unlikely to face such punishment but it would add pressure on the Prime Minister as she struggles to gather support for her draft Brexit deal. Opposition parties and a small Northern Irish party which props up May's minority government have also said they plan to reject the deal.
The prime minister will on Monday make another speech to MPs in an attempt to sell her deal.
Facing a hostile Commons chamber, the Attorney General told MPs to "grow up and get real" as he insisted he could not release his legal advice on Brexit in full because it would be "contrary to the national interest".
The party says it will accuse the government of being in contempt of Parliament if it does not release it.
Today the prime minister will resume her efforts to sell the deal, telling MPs about her visit to the G20 summit in Argentina over the weekend and the free trade deals the United Kingdom will be able to sign around the world after Brexit.
While lawmakers have voted for the advice to be published in full, Solicitor General Robert Buckland told the House of Commons on Friday that the government will provide just a "full and reasoned statement" on the legality of Brexit.
Opposition parties including Theresa May's DUP allies said the document and the Attorney General's statement failed to meet the terms of a vote demanding publication of the full legal advice and asked Speaker John Bercow to launch contempt of Parliament proceedings.
Attorney General Geoffrey Cox said he would have preferred the United Kingdom to be able to unilaterally terminate the backstop arrangement, while Theresa May's chief Europe adviser Olly Robbins admitted the situation was "uncomfortable".
Last month, MPs passed a binding Commons vote which required the government to present any legal advice it had received "in full", something May has ruled out several times.
"I will be talking with Members of Parliament ... and explaining why passing this deal in the vote that will take place in the House of Commons will take us to certainty for the future, and that failure to do that would only lead to uncertainty".
But the problem - seven days out from the vote - hasn't changed: Up to 100 Conservative MPs quite simply think this deal is so bad that they are not prepared to vote for it.
"And to deliver on that vote, we need to deliver a Brexit that respects the decision of the British people".
"He said he wanted to be on ITV so he could watch the final of I'm a Celebrity..."
If Theresa May's government lost a no-confidence vote, it would have two weeks to overturn the result with a new vote by lawmakers.
He said: "It is an uncomfortable position for both sides and the reality.is that there is not a Withdrawal Agreement without a backstop".