Allies of Theresa May have stepped up their attack on Andrea Leadsom, with one senior minister suggesting she could become the Tory equivalent of Jeremy Corbyn because of her lack of support in Parliament.
Employment minister Priti Patel, who campaigned for Brexit alongside Mrs Leadsom, suggested that the energy minister lacked the experience and broad appeal to win a general election.
Ms Patel, who is backing Mrs May's campaign, compared the Home Secretary to Margaret Thatcher and said her experience is "second to none".
In an interview with the Sunday Telegraph she warned that Mrs Leadsom could find herself unable to govern due to the lack of support from MPs, or win an election victory by appealing to swing voters.
"You win elections by having that broad appeal," she said. "Look at Labour right now, and the narrow appeal they have. We have to represent society as it is today and be a true voice for modern Britain and a positive Britain."
Mrs May secured her place on the leadership ballot by securing 199 votes from MPs, with Mrs Leadsom winning the support of 84 colleagues.
Ms Patel warned a victory for Mrs Leadsom could mean that the process of leaving the European Union would be harder to deliver, even though the energy minister backed Brexit and Mrs May had supported a vote to Remain in the EU.
"We have to govern," Ms Patel said. "To govern we have got to be able to carry the support of Members of Parliament. That's incredibly important. I don't need to give a re-run of what's happening with Labour right now."
Asked if Mrs Leadsom could become a Conservative version of Mr Corbyn, Ms Patel said: "We could end up in that situation. And then it becomes very difficult to govern and deliver the programme for Leave."
She added: "Right now we need an individual with a great deal of experience. She doesn't have that just yet, not yet. She is in government - but Theresa's experience is second to none."
Ms Patel said Mrs May was "on a par" with former prime minister Mrs Thatcher, the first female occupant of Number 10.
"She is on a par, there's no doubt about that, in terms of her ability, professionalism, her work ethic, but also what she wants for Britain. She wants us, not just to Leave, but also she has got the interests of our country firmly in her heart and Margaret Thatcher was exactly the same."
Former Tory leader Iain Duncan Smith dismissed the comparison between Mrs Leadom's position and that of Mr Corbyn when she secured second place in the MPs' vote on Thursday.
He told the Press Association: "Honestly, no comparisons with Corbyn. I have to tell you, this is a smart woman who has real intellectual capability, she is very easy, she speaks well, she's got real steel."
Ms Patel's comments came after Mrs Leadsom endured a barrage of criticism after appearing to suggest that being a mother gave her an advantage over her childless rival.
Mrs Leadsom said she was "disgusted" by the way her comments had been presented and insisted that she believed "everyone has an equal stake in our society", stressing that she did not want the issue of children to be a feature of the campaign.
In an interview with The Times, Mrs Leadsom said: "Genuinely I feel that being a mum means you have a very real stake in the future of our country, a tangible stake."
The Home Secretary has previously spoken about how she and husband Philip were affected by being unable to have children.
Business minister Anna Soubry said Mrs Leadsom's comments meant she was "not PM material" while Scottish Tory leader Ruth Davidson said there was a "gulf in class" between the two candidates and senior MP Sir Alan Duncan said the energy minister's remarks were "vile".
Armed forces minister Penny Mordaunt, a supporter of the energy minister's leadership bid, said The Times report was an attempt to "smear" Mrs Leadsom.