Ken Livingstone has blamed ‘The Establishment’ for Labour’s disastrous performance in the general election.
The former mayor said the same establishment had worked against him when he was in power.
Mr Corbyn has come under pressure to resign straight away but has said he will leave his role as Labour leader “in the early part of next year”.
Various party members have spoken out against Mr Corbyn and blamed his “catastrophic” leadership for a loss of Labour heartland areas.
Speaking to Andrew Castle on LBC on Sunday, former Mr Livingstone stepped to the Labour leader’s defence - and said establishment figures are “desperate to prevent Jeremy and John McDonnell getting into power”.
Asked what he meant by “establishment” the former Labour MP said: "The giant corporations, you actually look, big corporations on the internet."
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The presenter accused him of following a ‘conspiracy theory’ of the media trying to prevent Labour taking office.
Mr Livingstone, referring to when he became head of the Greater London Council during the Thatcher era, responded: "Immediately every Tory paper was running stories implying I was a Soviet agent, saying I support the IRA's bombing campaign. I was attacked three times on the streets because people believed all this. Literally, it just got worse and worse."
Asked if lessons could be learnt from the defeat - the party’s worst defeat since WWII - Mr Livingstone said: "The lessons that we need to learn that we've got to start properly regulating the media, we got to make sure lies are taken off the internet."
It comes as former Labour minister Alan Johnson said Mr Corbyn was “the main problem” at the election, calling him a “weak, self-regarding, pious man incapable of leadership.”
But Shadow Chancellor John McDonnell said he took the blame for the party’s defeat in the December election, telling the Andrew Marr he was sad about “wonderful” Labour MPs losing their seats.
No MP has yet formally announced they will stand for leadership - but Oddschecker lists Keir Starmer, Rebecca Long-Bailey and Angela Rayner as the front runners.
Shadow foreign secretary Emily Thornberry, Yvette Cooper and current shadow chancellor John McDonnell are also in the mix.