PARIS - The head of France's center-right UDI party said on Sunday he wanted presidential candidate Francois Fillon to quit the election race in favor of former prime minister Alain Juppe warning that if Fillon continued defeat was certain.

Once the frontrunner, Fillon is mired in a scandal over his wife's pay, and his campaign has been in serious trouble since he learned last week that he could be placed under formal investigation for misuse of public funds.

He is under growing pressure as party leaders prepare a crisis meeting for Monday to discuss the situation ahead of a March 17 deadline when all presidential candidates must be formally endorsed by at least 500 elected officials.

After a string of resignations among advisers and backers, the 63-year old former conservative prime minister was banking on a rally of supporters in Paris on Sunday to show his detractors that he remains their best hope to win the presidency.

"With Fillon it's a certain failure. This (rally) is an excess because you don't put the street up against the (state's) institutions," Jean-Christophe Lagarde told Europe 1 radio. "Even if there are 200,000 people, to win a presidential election you need 20 million people."

His UDI party, which represents between 2 to 5 percent of voting intentions, on Friday said it was withdrawing its support for the former prime minister.

Fillon pulled out of an early Monday morning radio appearance that aimed to discuss his campaign, the show's host said on Sunday. "Francois Fillon has officially canceled his appearance on Europe 1's morning program," presenter Thomas Sotto said on Twitter.

There was no immediate comment from Fillon's camp.

Opinion polls continue to show Fillon would fail to make the second round of the April/May election. Instead, centrist Emmanuel Macron is consolidating his position as favorite to win a second-round head-to-head against far-right National Front candidate Marine Le Pen.

Fillon has denied any wrongdoing and complained of judicial and media bias that amounted to a "political assassination".

His attack on the judiciary in particular has caused unease within his ranks and Sunday's demonstration has worried some on the right that it will be hijacked by hardline conservative movements.

His backers hoped to get at least 45,000 people at Sunday's rally to show he still carries favor among grassroots supporters.

In her first public remarks since the fake job allegations surfaced, Fillon's wife Penelope, told the Journal du Dimanche that her work activities had been real and insisted that her husband should go all the way.