Francois Fillon,  2017 presidential election candidate, visits a local police station in Meaux, France, Feb. 27, 2017.
Francois Fillon, 2017 presidential election candidate, visits a local police station in Meaux, France, Feb. 27, 2017.

PARIS - More cracks emerged in French conservative Francois Fillon's campaign for the presidency on Thursday, a day after news that he faces a formal investigation for allegations he misused public funds.

A flash opinion poll by Harris Interactive showed that only 25 percent of people now want him to continue as a candidate, down from 35 percent a month ago, while within his Republicans party there were more resignations after his decision on Wednesday to stay in the race.

While Fillon campaigned in southern France on Thursday ahead of a rally in the city of Nimes, poll favorite Emmanuel Macron unveiled his full centrist manifesto and far-right National Front leader Marine Le Pen was due to give a presentation on the role of the French state in the economy.

With less than two months to go to the April 23 first round vote, polls point to a second-round showdown on May 7 between Macron and Le Pen that the former investment banker would win.

Fillon, in third place and with a gap opening up between him and the two leaders, already suffered a major blow on Wednesday when key adviser Bruno Le Maire quit his campaign in protest at his decision to fight on.

On Thursday, deputy campaign director Sebastien Lecornu and adviser Vincent Le Roux followed Le Maire's lead, along with a number of more junior campaign staff.

Fillon denies any wrongdoing and stepped up his attacks on a French judiciary he insists is biased against him.

"I have been singled out by the judicial system. It's as if I had to be brought down at all costs," he said in an interview with the newspaper Midi Libre.

Fillon is to be questioned by investigating magistrates on March 15 with a view to being put under formal investigation.

Supporters plan to organize a rally in Paris on Sunday in support of his campaign.

Sources in the Fillon camp have said there was a strong push by some in the party on Wednesday to have former prime minister Alain Juppe stand in Fillon's place, but the plan was vetoed by Nicolas Sarkozy, the former president.

George Fenech, a lawmaker who led a failed rebellion against Fillon last month, confirmed on Thursday that he was among those wanting Juppe to stand in Fillon's place.

"Unhappily, I am convinced that Francois Fillon is about to fall," he told France Info radio. "It seems to me that today only he [Juppe], with all his experience, can carry the flame."

Juppe, 71, insists he has no interest in replacing Fillon.