The Prime Minister faces his final days in office, as one of Rishi Sunak or Liz Truss will be declared Conservative Party leader on Monday.
But Mr Johnson's career appears to be far from over.
Lord Marland, who led Mr Johnson’s London mayoral campaign, said there was a “distinct possibility” that he would aim for No 10 again in future.
The PM's close friend said: “The scenario could be that we lose the next election, we could be looking for a leader who can win elections – and of course Boris Johnson has that.
Prime Minister Boris Johnson
Peter Nicholls
"As he said to me the other day, he wants to go and put hay in the loft, in other words to build up his bank balance so that he can afford to pay for the lifestyle that he has created.
“I think once he's done that, if he is still a member of Parliament and hasn't been found to have behaved incorrectly by the standards committee – which is a possibility – I think he does have that opportunity."
Lord Marland added that Mr Johnson’s departure would be a "great loss" to politics but "hopefully only temporary".
His comments in The Telegraph come as legal advice, commissioned by the Cabinet Office, is expected on Friday to call into question the legitimacy of the Partygate inquiry.
The advice, by Lord Pannick, QC, is said to show that investigating ministers for misleading the Commons “in good faith” would create a chilling effect and would “paralyse democracy.”
Labour MP Chris Bryant, chair of the Committee on Standards, questioned why the Government is paying for legal advice for an individual.
He said: “I think it’s very odd that they’re announcing that it’s coming.
Prime Minister Boris Johnson outside Downing Street
Dominic Lipinski
“Secondly, I think it’s very odd that the Cabinet Office seem to have commissioned this advice on behalf of a private individual, namely the Prime Minister – that seems a very odd way to behave.
“Thirdly, it’s very odd for a member of the House of Lords to tell the House of Commons what to do."
He concluded in an interview on BBC Radio 4's Today Programme: “And fourthly, I think from what I’ve seen so far – and just like everybody else, I’ve not seen the actual advice – but I think it’s completely misleading or misjudged, because of course you want ministers when they stand up in the House of Commons to be careful about what they say, to make sure that what they are saying is the truth.”