"She is here to deliver Brexit in phase one and then she will leave to make way for new leadership for phase two," he told reporters, AFP reported.
May is under increasing pressure from MPs and activists in her Conservative party unhappy over Brexit, which was due to take place on March 29 but has been delayed twice.
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.
But her critics fear that with Brexit now delayed to October 31, she might stay in office for many more months.
Anger at her leadership has flared up following last week's dismal local election results, and the chairman of the 1922 committee of Conservative MPs, Graham Brady, met May on Tuesday to relay their concerns.
Earlier on Wednesday, May was confronted in the House of Commons by a Brexit-backing Conservative MP, Andrea Jenkyns, who said: "The public no longer trust her to run Brexit negotiations."
May responded by noting that she had agreed a deal with the EU to leave, but MPs had rejected it three times.
"This is not an issue about me and it's not an issue about her. If it were an issue about me and the way I vote, we would already have left the EU," she said.
May has for several weeks been in talks with the main opposition Labour party to find a compromise deal, but there is no sign of progress yet.
A Labour spokesman said Wednesday the party hoped to establish "in the next few days" whether a deal was possible.
If their talks fail, May has pledged to allow the House of Commons to decide on a new strategy in a series of votes.
The EU has agreed to delay Brexit until October 31 to allow British politicians to try to agree a way to leave that minimizes the impact of the split.
May on Tuesday reluctantly accepted that Britain will take part in European parliamentary elections on May 23, almost three years after voting to leave the EU.
But she still hopes a divorce deal can be agreed to allow Brexit by June 30, which would mean British MEPs would never have to take their seats.