Micheal Martin can only survive as Fianna Fail leader if he becomes Taoiseach in the coming weeks, senior TDs have told the Herald.
Mr Martin's future is on the line as efforts to form a government continue, with several Fianna Fail front-bench TDs saying he could not continue as leader if Fianna Fail is not leading the next government.
"The only way he can survive is becoming Taoiseach, and that's the elephant in the room," said one.
Another front-bench TD ack- nowledged it would be "the end of the road" for Mr Martin if he is not Taoiseach.
"There's a bit of discussion around it. People are beginning to say that if he doesn't end up as Taoiseach, we'll have to start looking at our options," the TD said.
A third front-bench TD said: "It's not a question of would there be a heave. Why would he want to lead us into opposition or into a second election?"
Another Fianna Fail source claimed the party was "ill- prepared" for the election.
"If Micheal isn't Taoiseach, it's goodbye," the source added.
Fianna Fail's parliamentary party will meet in Leinster House this evening.
Despite apparent unanimity on opposition to entering talks with Sinn Fein after last week's meeting, two senior TDs told this newspaper they would not be opposed to the idea if no government can be formed in the coming weeks.
"I would be one of the people least averse to talking to Sinn Fein in the party, but it does present me with awful difficulties and the supporters are split," one of them said.
The other senior TD said: "If Fine Gael stick to their position, Micheal Martin might have to eat humble pie and go and talk to Sinn Fein."
Sources do not expect serious efforts to form a government until after tomorrow's proceedings in the Dail, but the stakes are perhaps highest for Mr Martin. Another Fianna Fail front-bench TD said they believe Mr Martin will be gone as party leader if he does not become Taoiseach in the coming weeks.
The TD said the party is happy to let him go through the government formation process.
Ultimately, it may come down to a deal with Fine Gael, which the source said would be "unpalatable" for everyone.
However, the TD added that "a general election would focus minds a lot more" and party members would say "let him be Taoiseach".
A different front-bench TD said Fianna Fail wants Mr Martin to become Taoiseach, and added: "I trust him to do the right deal."
Mr Martin is likely to outline his thinking on the next steps at this evening's parliamentary party meeting.
The focus has turned on him after Taoiseach Leo Varadkar said Fine Gael is preparing for opposition.
He left the door open to a possible grand coalition with Fianna Fail if Mr Martin and Sinn Fein's Mary Lou McDonald are unsuccessful in their respective government formation bids, but only as a "last resort".
All of the main party leaders are expected to put their names before the Dail when it convenes tomorrow in votes to elect the next Taoiseach, but none will be successful.
This will force Mr Varadkar to tender his resignation to the President, but he will remain as caretaker until a new government is formed.
The Social Democrats cancelled a planned meeting with Fine Gael yesterday, accusing Mr Varadkar's party of "game playing".
It came after Mr Varadkar's remarks the previous evening on his intention to go into opposition.
A Social Democrats statement said: "Clearly, Fine Gael's intention is to engage in shadow boxing for the coming weeks and we've no interest in participating in such a charade."
A senior Fine Gael source said the Social Democrats' decision was "bizarre" and accused the party of "bad manners" and of being "discourteous".
Green Party leader Eamon Ryan has cast doubt on the prospect of an exclusively left-wing government, saying it is hard to see how it would be stable. It came after he met Solidarity-People Before Profit TDs on Monday.
He said he told them it takes three or four years to do anything, but questioned how such a government would survive three months.
Mr Ryan cited more ambitious carbon emissions reduction targets of 7pc a year among demands that the Green Party would make of potential coalition partners. The current target is a 2pc a year drop.
Meanwhile, Sinn Fein TD Pearse Doherty led his party's negotiation team in a meeting with senior civil servants at Government Buildings as it seeks to transform its manifesto into a Programme for Government.
Mr Doherty said Sinn Fein is intensifying its talks with other parties and Independents, with plans to meet today.