Paris: Beleaguered French politician Francois Fillon on Sunday declared "no one can stop" his bid for the presidency after a mass rally attended by thousands in Paris.
The centre-right candidate insisted he would not be standing down during an interview on French television, despite growing calls for him to quit the race, BBC reported.
Fillon,63, faces a criminal investigation over payments made to family members. He suffered a severe setback this week after The Republicans party senior chiefs suspended their support for his bid and are mulling a Plan B in which the moderate conservative Alain Juppe is well placed to represent the right-wing party in the upcoming presidential election.
Juppe has announced he will be making a statement on Monday.
Fillon had earlier told tens of thousands of supporters he would be cleared over allegations he had paid his family for work they did not do.
These allegations have resulted in Fillon's popularity slipping in opinion polls, and Sunday's rally was seen as a crucial test, with senior figures in his party said to be eyeing up a replacement.
Just before the rally Christian Estrosi, a close ally of former President Nicolas Sarkozy, told BFMTV that senior Republicans would propose an alternative candidate in the coming hours.
However, he said it was important "not to humiliate" Fillon and allow him a "dignified" way out.
The Republican party will hold crisis talks on the candidacy on Monday.
But Fillon was in a defiant mood during in an interview on French television network France 2 on Sunday evening.
"No one today can stop me being a candidate," BBC quoted him as saying.
He said he was "not autistic" and was able to listen to criticism and understand the difficulties his campaign faced.
However, he rejected the idea of being replaced by 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," Fillon said.
"No one has the power to force me to withdraw... It is not the party that will decide. It's not regional presidents or former primary candidates who will make the decision for me," Xinhua news agency quoted Fillon as saying on France 2.
"It's not behind the scenes that things will happen, but before the French," he added.
A Kantar Sofres-Onepoint poll released on Sunday continued to show Fillon losing his bet to overturn sliding popularity in the wake of "PenelopeGate". It showed that the former Prime Minister is set to collect 17 per cent of the vote, down by 3 percentage points from a previous survey.
Fillon, once the favourite to win the election, has been under fire since a French satirical weekly Le Canard Enchaine, on January 25, reported that he had paid his wife and two of his five children about one million euros ($1.062 million) for their jobs as parliamentary assistants. However, there was no evidence showing that Fillon's wife had really worked.
He will appear before investigation magistrates on March 15, put under formal investigation.