The former prime minister said Labour needed to abandon Mr Corbyn’s “revolutionary” politics to counter Mr Johnson’s “right-wing populism” if he wins the race to succeed Theresa May.
Ms May has announced she will stand down once she has delivered on Brexit.
Mr Blair said Mr Johnson was a “formidable campaigner” who would pose a significant challenge to Labour at a general election.
In an interview with HuffPost UK, the ex-Labour leader said the party needed to offer a “sensible, coherent alternative” that would appeal to Conservative voters “repelled” by the former foreign secretary’s role in Brexit.
Mr Blair, who has long been a critic of Mr Corbyn, said it would be a “bizarre analysis” to suggest such people could be won over by a “revolutionary alternative from the left”.
“If you have a Boris Johnson-led Conservative Party, he’s a formidable campaigner, he’s an interesting personality, he can get out there and do his stuff, for sure,” he said.
“I have absolutely no doubt that if you have a right-wing populism against a left-wing populism in this country, the right-wing will win. So it depends where we [Labour] stand.
“If we stand in a reasonable position, where you have many Conservative voters voters that will feel repelled by a Boris Johnson premiership, particularly after the part he’s played in Brexit, but you’ve got to be in a position where those people feel it’s safe to vote for you.
“You suddenly offer them a revolutionary alternative from the left, what makes you think the people who voted Tory are suddenly going to go for that? It’s a bizarre analysis of their psyche.”
It comes as Mr Corbyn told the Daily Mirror his party was “ready for a general election, whenever it comes”.
He said: “A general election would give us the chance to remove this incompetent and failed Tory government.
“Whether people voted Leave or Remain, they face problems of falling living standards, rising job insecurity and cuts to essential services across the country. Labour will bring people together.”
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