Theresa May has suggested that she may demote Boris Johnson in a cabinet reshuffle in an interview with The Sunday Times.
She is planning the reshuffle after the European Council meeting on 20 October to ensure that she has "the best people in her cabinet", Tory sources told the newspaper.
A cabinet reshuffle raises questions about the future of Foreign Secretary Boris Johnson, who has been accused of trying to oust May.
Asked what would happen to Johnson in a cabinet reshuffle, May said: "It has never been my style to hide from a challenge and I'm not going to start now. I'm the PM, and part of my job is to make sure I always have the best people in my cabinet, to make the most of the wealth of talent available to me in the party."
But in his Sunday Telegraph column addressing "the elephant in the room", Johnson asserted his loyalty to May and called on voters and Tory MPs to get behind her.
"Above all the people of this country want us to get on and deliver Brexit - and we need Theresa to do it. I have worked with her for years and I can tell you that once her mind is made up there is no one more implacable and determined in pursuing what she believes is right for Britain," he wrote.
"Let's get on with it, get behind the Prime Minister, and govern as dynamic one nation conservatives in the interests of the whole country," Johnson urged at the end.
The prime minister is facing mounting pressure to stand down after a "disastrous" speech at the Tory party conference on 5 October.
The speech was supposed to assert May's authority over her party after several turbulent months, but the prime minister struggled to communicate her vision for Britain post Brexit as she was plagued by a coughing fit and interrupted by a prankster.
After May's poor performance, former party chairman Grant Shapps said there should be a leadership contest, telling reporters that at least 30 other Tory MPs agreed with him.
But May shrugged off the idea that she may be ousted by backbench Tories and said that the country needs "calm leadership" to guide it through upcoming Brexit negotiations.
"That's exactly what I'm providing, and I'm providing that with the full support of my cabinet," she told reporters when asked about Shapps' bid to force a leadership contest.