Labour MPs should hold a vote to choose either Andy Burnham, Yvette Cooper or Liz Kendall to take on Jeremy Cobyrn in the party's leadership election, Labour's John Mann has said.
On Wednesday Tony Blair launched a scathing attack on Corbyn, warning Labour faced "annihilation" if it picked the leftwinger to succeed Ed Miliband.
Corbyn is now seen as the frontrunner in the race, much to the dismay of those in the centre and on the right of the party.
Mann told BBC Newsnight the idea that Corbyn was "unstoppable" was wrong, but said two of the three other candidates needed to drop out.
"It needs to be a head-to-head now. Jeremy Corbyn is framing the debate. It is him verses the rest. What there needs to be is the rest needs to have one candidate.
"The three of them can agree, let the MPs renominate informally. Whoever gets the most nominations amongst those three should stand as the candidate."
Mann, who is backing Cooper in the contest, said there should then be a televised debate to make sure Corbyn was "put under some proper scrutiny".
Labour MP John Mann has called for a head-to-head leadership contest
Writing in The Guardian, Blair said the Labour party was in a danger "more mortal today than at any point in the over 100 years of its existence".
"The party is walking eyes shut, arms outstretched, over the cliff’s edge to the jagged rocks below," he said.
But Labour deputy leadership candidate Angela Eagle also told Newsnight that Blair should "calm down a bit" and warned "apocalyptic language" was not very helpful.
Corbyn's campaign told The Huffington Post in response to Blair's comments: "We are keeping our campaign positive and remain focussed on our policies which offer the sound economic choice of investment and growth, not the politically driven agenda of austerity and cuts preventing economic recovery."
Labour revealed this evening that in total 610,753 people applied to vote in its leadership election, with around 400,000 people having signed up since the election.
The party indicated some may still be denied a vote if they are found to be Labour opponents trying to unfairly tip the contest in one candidate's favour.
Verification process continues, but total figs of those who applied for a vote: Affiliated: 189,703, Registered: 121,295, Members: 299,755— Labour Press Team (@labourpress) August 12, 2015
On Wednesday, Labour MP Simon Danczuk said Corbyn would face a coup against him by his MPs on the first day after he was elected leader.
Danczuk, who has called on the contest to be halted, said Corbyn would not last in office for "about 12 months". Asked on LBC radio if the plotting would begin on "day one", he said: "Yeah, if not before. As soon as the result comes out. People in the PLP [Parliamentary Labour Party] aren't going to put up with it. "
The Rochdale MP, who was also a harsh critic of Ed Miliband, said he would not put up with the "crazy leftwing policies" advocated by Corbyn.
Labour had to extend the deadline for people to register to vote in the leadership contest from midday until 3pm on Wednesday after its website crashed. Ballot papers will be sent out on Friday and the result will be announced on September 12.
Commenting at the end of registration to participate in the leadership election, Corbyn said: "The response to the Labour leadership race from party members and supporters, longstanding and new, is proof of the optimism in the possibility of a popular, modern alternative to the Conservative government.
"All of our focus must be on channelling this extraordinary movement towards a united party that is able to find its confidence and defeat the Conservatives in 2020.
"I particularly want to pay tribute to the Labour Party’s staff who have worked so hard to deliver a robust selection system in totally new circumstances. The professionalism and commitment of the party’s staff shows our movement at its best."
The party has seen a surge in the number of people able to vote in its leadership contest since the election.
However some in the party are worried that it is being infiltrated by the hard left who are actually opposed to Labour values.
Around 1,200 members or supporters of another party have already been excluded from voting in the leadership contest, including hundreds who stood against Labour in local or national elections.
They included 214 from the Green Party, 37 from the Trade Unionist and Socialist Coalition, 13 Tories, seven from Ukip and one from the BNP.
On Tuesday a YouGov poll for The Times showed Corbyn now has a staggering 32-point lead over Andy Burnham, his nearest rival.
The left-wing candidate is poised to win in the first round of voting having polled 53 per cent of the vote - a 10 per cent surge on a month ago. Corbyn, who wants Trident scrapped and industries re-nationalised, has pulled well ahead of Burnham on 21 per cent, Yvette Cooper on 18 per cent of the vote, and Liz Kendall with just eight per cent.
YouGov President Peter Kellner has said he would be "astonished" if Corbyn did not win the leadership race but added: "I have seldom released a poll with as much trepidation as I have done this time."