The Shadow Chancellor refused to rule out becoming interim leader during a press conference on Monday. He told FT: “It’s not going to happen because we’ll be having a majority Labour government.” Mr Corbyn has also refused to say whether he would resign as Labour leader if Boris Johnson this Thursday’s poll.
But if some opinion polls are correct in their suggestions that the 70-year-old is on course to lose two general elections in succession, Mr Corbyn could finally crumble under the pressure from some of his own party to step down.
If this did happen, the deputy leader would then fill his shoes, but the position is currently vacant after Tom Watson stepped down as an MP just before the election.
And Mr Mcdonnell has been very visible during the election campaign after taking part in 20 TV and radio interviews – more than any other colleagues.
One of his allies told the FT: “If you think who else could take that temporary role, who is there? John is probably the most likely to do the job, he’s seen as an honest broker between the various factions.” said one of his allies.
Social media users have been quick to suggest Mr McDonnell is eyeing up the top job.
Anthony Thomas wrote on Twitter: “Beware of John Mcdonnell and his plan to lead a post election leadership coup to oust Corbyn similar to the way he and Livingstone seized control of The GLC.”
Another person added: “The plan for John McDonnell to take over as Labour’s interim leader explains why there was a plot against Tom Watson this autumn.”
Mr McDonnell has spent the election campaign chairing he daily morning campaign meetings while Mr Corbyn has been touring the country giving speeches or rallies to Labour supporters.
He would also give some MPs more senior jobs, including Rebecca Long-Bailey.
She is currently shadow business secretary but could be promoted to shadow chancellor.
Laura Pidcock, shadow employment minister, and Angela Rayner, education secretary, could also be given bigger roles.
When asked whether he would resign if Labour lost the election earlier this week, Mr Corbyn said: “We put forward a positive manifesto with a fully costed programme and I am taking that message out all over the country.
“That message is getting home to people. They realise this Thursday is a straight choice: do you want to carry on with austerity and underfunding of public services or do you want a Labour government that will tax fairly to fund properly.”
Mr Corbyn was asked about shadow chancellor John McDonnell’s claim that some of Labour’s opponents “hate” the people of Britain.
“I think it is pretty clear they have a sense of contempt for the poorest working class communities across Britain.
“They have seen their local services cut because of the underfunding of local government and have seen so many people lose good jobs and end up on zero hours contracts or insecure employment. Things must change in this country.”
Mr Corbyn also said he “never commentated” on opinion polls, which some have suggested is leading to a Conservative victory.
He said: “Labour’s going to win on Thursday. I am concentrating solely on getting the message out all over Britain between now and Thursday when we can elect a Labour government.”
There have been tensions between Mr Corbyn and many of his own MPs ever since he became leader.
There was even an unsuccessful attempt to bring him down in a coup in the summer of 2016.