The campaign is one of the most unpredictable in the country's history as almost 40 percent of voters have yet to make their final choice amid a topsy-turvy campaign dominated by a fraud investigation into Fillon.

Once the frontrunner, the former prime minister has fought off pressure from his The Republicans party to step aside before Friday's deadline when all presidential candidates must be formally endorsed by at least 500 elected officials.

His main rival for the party ticket, Alain Juppe, opted not to challenge him, even if theoretically he could still get 500 backers by 1800 local time (1700 GMT).

Fillon, 63, has faced down his critics and insisted he will fight on despite an Odoxa opinion poll on Friday showing that three-quarters of French voters want him to pull out of the race.

The fraud investigation into Fillon widened on Thursday to include luxury suits he received as gifts. He was already placed under formal investigation earlier in the week on suspicion of misusing public funds linked to salaries he paid his wife and children.

Fillon, far-right leader Marine Len Pen, independent centrist Emmanuel Macron, Socialist candidate Benoit Hamon, far-left firebrand Jean-Luc Melenchon and two lesser-known candidates have already reached the endorsement target.

Another four at least could also reach the goal when the Constitutional Council publishes its final sponsors list.

It will confirm the candidates on Saturday.

Melenchon categorically ruled out on Friday quitting the election race in favour of Hamon.

Since news of the Fillon scandal emerged on January 25, he has tumbled from being the favorite to third place in opinion polls, a position that would eliminate him in the first round on April 23.

The polls point to a May 7 run-off between Le Pen and Macron, with the latter convincingly winning that duel.

A weekly Ipsos SopraSteria poll for Le Monde on Friday showed Fillon losing more ground to Le Pen and Macron.

More about: #France   #Fillon