In March, she vowed to take Britain out of the European Union but then to hand over to another leader to negotiate future bilateral ties with the bloc.
She is immune from a leadership contest until December after surviving one past year.
He said May wanted to hold votes in parliament on detailed Brexit legislation before Britain is due to hold elections for the European Parliament in two weeks.
The left-of-center party executive was meeting Tuesday to determine what to put for the parliamentary election that is now happening in just over only 3 weeks.
Mrs May is set to meet senior figures from the powerful 1922 Committee of backbench Tories to discuss her departure plans.
May replied: "This is not an issue about me and it's not an issue about her".
He said: "If indeed the Conservatives get something like 15 percent of the vote, which is what they are now at, the days of the Prime Minister, which are already, frankly seemingly limited in scope, may become even more limited".
He will reaffirm the party's pledge to offer voters a chance to have a say on a deal, saying: "But we can never accept the government's bad deal or a disastrous no deal".
Ongoing talks with Labour to pass an agreement have so far failed to break the deadlock - leaving political parties on both sides of the Brexit divide gearing up for what has been described as a "zombie" poll because the government is still planning to leave the European Union within months.
May yesterday reluctantly accepted that Britain will take part in European parliamentary elections on May 23, nearly three years after voting to leave the EU.
The impasse forced her to seek a delay to the Brexit deadline which now stands at 31 October.