Jordan Bardella served as the spokesperson for National Rally, the far-right party under Marine le Pen. But ahead of the election next year, Mr Bardella issued a dire warning to Mr Macron and claimed eurosceptic Ms Le Pen will win.
Tweeting out a video of him on the French news outlet LCI, Mr Bardella said: “Many French people believe she is legitimate, that she has demonstrated her soundness, that she has toughened up, that she was right very early on before everyone else.
“I am convinced that Marine Le Pen will win this presidential election.”
In the video, Mr Bardella said the leader of the National Rally has “toughened up” following her defeat in 2017.
He said: “After 2017, Marine Le Pen has learned from her mistakes. She has toughened up since that defeat to prove that she is the right leader of Rassemblement National and the right candidate to lead France.
“I am convinced that Marine Le Pen will win this presidential election.
“Many people used to say that her ideas were extreme and they rejected her, but now they realise that we were right about many topics such as immigration, Islamism, globalisation.”
Mr Bardella’s comments come after a new poll found police officers and soldiers are likely to vote for Ms Le Pen over Mr Macron.
The survey found around 44 percent of police and military personnel would vote for Ms le Pen in the first round of the presidential election next year.
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Up to 52 percent said Ms Le Pen “really wants to change things” compared to the French President who only received 32 percent of votes.
The poll came as a debate over insecurity is in full swing across France, following the deaths of police officers in Rambouillet and Avignon.
Earlier this week, Mr Macron was warned there could be a “civil insurrection” in France unless his government does not get a grip on the rising Islamism crisis.
Penned by ex-military figures, an open letter warned France is facing civil unrest following a number of fatal attacks by Islamic terrorists.
The military veterans accused Mr Macron of treating senior military figures as “factious when their only fault is to love their country and to mourn its visible downfall”.
The letter read: “We see hatred for France and its history becoming the norm.”
Before warning the “chaos and violence” in recent events across France will come from a “civil insurrection” rather than a military coup.
Ms Le Pen welcomed the letter and said: “I invite you to join us in taking part in the coming battle, which is the battle of France.”
However, her support was met with criticism on both the Left and Right.
The survey was carried out from April 9 to 15 by Ipsos among a cohort of 144 members of the security forces out of 10,000 French people questioned, as part of a Cevipof survey.
Additional reporting by Maria Ortega