Keir Starmer summoned his dwindling band of supporters to Chequers for a 'survival summit' on Friday.
As pressure grows on him to quit, Labour sources said the Prime Minister was in emergency talks aimed at fending off imminent leadership challenges.
Ministers and backbench MPs are discussing options to force out Sir Keir following next month's local elections, which polls suggest will lead to disastrous losses for Labour.
Options circulating include requiring Sir Keir to announce a departure date in the coming months, which would allow Greater Manchester mayor Andy Burnham time to return to Westminster where he could stand for leadership.
Others favour forcing Starmer out and installing a caretaker leader, such as Foreign Secretary Yvette Cooper, who could serve for up to a year.
The PM's supporters are drawing up plans for an immediate fightback in the wake of the May 7 elections, including unveiling a legislative programme in the King's Speech six days later. Allies believe any bid to depose the PM in this period would risk causing embarrassment to the King, and also hope to prey on splits among mutinous MPs about who should take over.
One source said: 'It would create chaos to have a leadership contest where there is no clear successor. There's a risk we end up with a Left-wing version of Liz Truss, which would be the end of the party at this point.'
A government source denied the meeting amounted to a 'survival summit', saying it was held to discuss 'framing around the King's Speech'.
Sir Keir Starmer summoned supporters to what has been billed a 'survival summit' at Chequers on Friday
Loyalists including the PM's Chief Secretary Darren Jones and the Work and Pensions Secretary Pat McFadden are among those said to have attended.
The PM's spokesman said Sir Keir is committed to staying on as PM until the election 'and beyond'. But one Labour MP told the Daily Mail that Sir Keir was 'finished', adding: 'We are heading for a bloodbath next month. There is no way that he will survive it.'
The Guardian reported that Labour MPs have 'coalesced' around Mr Burnham, who is said to be in discussions with Angela Rayner about a potential 'dream ticket'.
Sir Keir's position has worsened in recent days in the wake of the Peter Mandelson scandal. The PM now faces a potential investigation into whether he lied to parliament when he claimed 'no pressure whatsoever' was put on the Foreign Office to permit the controversial appointment.