France's centre-right Republicans are to meet on Monday evening to try to resolve the crisis over their presidential candidate.
Francois Fillon faces allegations that members of his family were paid taxpayers' money for fictitious jobs.
Mr Fillon has denied wrongdoing as support for him has dropped in opinion polls ahead of next month's vote.
Alain Juppe, who is tipped to replace him if he withdraws, is due to make a statement in the morning.
At the party meeting, Republican heavyweights will try to bridge the growing cracks between their candidate and his former rivals, and find a way forward, the BBC's Lucy Williamson reports from Paris.
The battle between Mr Fillon and his party may be entering the end game, she says.
Several senior figures are expected to announce their support for Mr Juppe's nomination in the coming hours.
Pressure built on Mr Fillon in the past few weeks, as desertions by political allies and senior campaign staff multiplied.
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At a mass rally in Paris on Sunday, a defiant Mr Fillon told thousands of supporters that "no one can stop" his bid for the presidency.
The centre-right candidate insisted he would not be standing down during an interview later on French television.Image copyright AP Image caption It is not clear whether the numbers at the rally will be enough to save Mr Fillon's campaign
At the rally, he rejected the idea of being replaced by Mr Juppe, his rival in the primaries last year.
"If they had wanted Alain Juppe's project, then they would have voted for Alain Juppe in that election," Mr Fillon said.
He said he would be exonerated when an impending criminal investigation got under way, and it would be the turn of his accusers to feel ashamed.
For weeks he has fought allegations that his wife, Penelope, was paid for a number of years for work that she did not do as his parliamentary assistant.
However Mrs Fillon, who insists she did work for husband, told French magazine Journal du Dimanche on Saturday that "everything was legal and declared".
Also under scrutiny are claims that two of the children, Marie and Charles, were paid by their father's office for legal work though they had not yet qualified as lawyers.
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