According to a report in Libération newspaper - based on accounts from hundreds of readers - many left-wing voters no longer support Mr Macron. Political science professor Rémi Lefebvre has now said left-wing voters feel "hurt and humiliated".
Mr Lefebvre said: “Left-wing voters feel hurt and humiliated.
"They feel they are being forced to vote for a candidate who has not respected them.”
Brexiteer group Leave.EU has said people are waking up to the "evils of globalism and EU corruption".
They tweeted: "Things go from bad to worse for Brussels lapdog Emmanuel Macron, with left-wingers abandoning him in droves.
"People across Europe are waking up to the evils of globalism and EU corruption!"
Another person tweeted: "Le Pen is mightier than EU!"
Someone else said: "French independence from EU!! Works for me!"
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Another person said left-wing politicians are "forever trying to bully and manipulate rational people".
While someone else simply said: "Macron needs to get the boot!"
Back in 2017, Mr Macron beat Ms Le Pen by a wide margin, securing two-thirds of the vote due to the huge support from the left-wing of French politics.
A poll in January found Ms Len Pen was just two points away from securing the French presidency in the 2022 election.
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Even a top ally to Mr Macron admitted Ms Le Pen could win the French Presidency next year.
Earlier this month, French Finance Minister Bruno Le Maire told BFM TV: "The election of Marine Le Pen, as we all know, is a political possibility. It must be fought.
"Fought with ideas, convictions, results, with men and women who are committed.
"I hope that in this fight against Marine Le Pen, our ideas will prevail. It is in the field of ideas that we must go, in the field of what we want for France, of the European construction.
"In 2022, I would like Emmanuel Macron to be a candidate for the election, for presidency of the Republic, and I will be at his side to ensure that he is re-elected."