The former Chancellor, who is now editor of the London Evening Standard, told BBC One’s The Andrew Marr Show: “It is just how long she is going to remain on death row.”
He added: “I think we will know very shortly. We could easily get to the middle of next week and it all collapses for her.”
On the Sunday Politics show, Dominic Raab, a backbench Tory MP was asked about Mr Osborne’s comments and said: “George has made the transition from a Conservative politician to mischievous journalist with great ease.
“Actually, most MPs when they listen to that will think him disloyal, unprofessional and frankly pretty self-indulgent. In reality I think that will shore up support amongst a lot of MPs for Theresa May.”
Ms May’s grip on power appears far from secure, despite a potential deal with the Democratic Unionist Party to support her in Parliament.
Downing Street initially said an outline agreement on a “confidence and supply” arrangement had been reached with the DUP.
But no deal has yet been finalised and talks on the arrangement will continue during the week as Ms May desperately tries to shore up her position after losing her Commons majority in the election.
In another sign of the dangers facing Ms May, Sunday papers reported that Boris Johnson was either being encouraged to make a leadership bid in an effort to oust her, or actually preparing one – a claim dismissed as “tripe” by the Foreign Secretary.
The Mail On Sunday reported that Mr Johnson was preparing a leadership bid, with a close ally saying it was "go, go, go", adding: “We need Bojo.”
Mr Johnson tweeted to say: “Mail on Sunday tripe - I am backing Theresa May. Let’s get on with the job.”
But The Sunday Times said Mr Johnson had been pressed by five Cabinet colleagues to oust Ms May.
An ally of Mr Johnson told the newspaper: “We are facing a populist and they have realised we need someone who can talk to the people.
“We need a Brexiteer. Boris is the only option with the liberal values, Brexit credentials and popular appeal.”
A spokesman for Mr Johnson said: “The Foreign Secretary is 100 per cent supporting the PM and working with her to get the best deal for Britain.”
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies