"Even if they come back in October, November, and they say, 'this flimsy bit of paper is what you're going to have to agree to, otherwise there'll be no deal', we're not going to agree to either of those," she said.
One of these is that it delivers the "exact same benefits" that Britain has as a member of the EU's single market and customs union.
The prime minister and the EU have both said this will not be possible, and commentators have long believed Labour will vote against the government.
The prime minister hopes to reach a deal in mid-October or early November, ahead of Brexit in March 2019. The agreement must then be approved by the House of Commons, where she has only a slim majority.
It is unclear what would happen if MPs reject the deal.
But legislation is already in place to implement Brexit, raising the possibility that Britain crashes out without any agreement on new terms with the EU.
May would also likely face a leadership challenge in her own party, although that would not automatically cause a new election.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)