According to a new opinion poll conducted by Opinionway-Orpi for financial newspaper Les Echo, and Radio Classique, Fillon’s recent problems over employing family members is having an impact on his support.
The centre-right candidate now has 58 per cent of potential votes – as opposed to 60 per cent on Friday - as opposed to 42 per cent for Marine Le Pen, as opposed to 40 percent on Friday.
Le Pen has also gained two points on independent candidate Emmanuel Macron.
As it stands, in the first round of voting Marine Le Pen still leads the pack with 26 per cent ahead of Emmanuel Macron (22 per cent) and Francois Fillon (21 per cent).
The socialist candidate Benoit Hamon stands at 15 per cent and hard left candidate Jean-Luc Mélenchon (11 per cent).
The poll was carried out over the weekend from a survey of 1.590 registered voters.
Meanwhile, Fillon vowed to "fight to the end" at a rally on the Indian Ocean island of Réunion Sunday as a newspaper claimed that judges could order action against him this week.
The embattled French presidential candidate faces allegations that members of his family held fake jobs as parliamentary assistants for him.
"I am being attacked 24 hours a day but I also receive countless messages of support," Fillon told an election rally on Réunion, a French overseas department. "I will fight to the end because my programme is the only one capable of reviving France."
Fillon is due to arrive back in France later today and visit the Seine Saint-Denis department that has been the scene nightly protests since the over the alleged police rape of a 22-year-old black man identified as Théo.