Ms Le Pen, the leader of far-right party Front National, is an ardent eurosceptic and had pledged to hold her own Brexit-style referendum if she is victorious in the presidential race.
Michael Hessel, a political economist at Absolute Strategy Research, claims a Le Pen victory could bring Brussels to the breaking point.
He told CNBC: “It’s difficult to imagine how the European Union could function should such a eurosceptic as Le Pen be at the helm of one of its major economies… It would likely precede its fracturing.”
Speaking to Channel Four News, Mr Macron echoed the economist’s views, warning a Le Pen victory would leave the bloc struggling to function.
Emmanuel Macron says Marine Le Pen will 'kill' the EU if she becomes French president
If she wants to implement what she proposes on the European Union she will kill the single market
“If she delivers what she proposes, she will kill the European Union,” he said.
“[She will do it] de facto, because she wants diversion – on immigration, on the economy, finance.
“If she wants to implement what she proposes on the European Union she will leave. She will kill the single market because it’s not compatible with a single market.
“So, for sure she will decide to leave.”
Opinion polls suggest Ms Le Pen is likely to top the first round of the presidential poll on April 23 but then lose the May 7 run-off to conservative Francois Fillon or centrist Mr Macron.
But in a race that is turning out to be the most unpredictable France has known in decades, the Front National hopes its recent rally in Lyon, where Ms Le Pen spelt out her electoral agenda, will help convince voters who have traditionally backed mainstream parties to give her a chance.
In her passionate speech, the far-right leader vowed to put French citizens first by curbing migration and holding a referendum on the country's EU membership.
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She insisted she will stop France from being “globalised” while ensuring citizens have more rights than foreigners.
Get to know Marine Le Pen Sat, January 28, 2017
Marine Le Pen is a French politician who is the president of the National Front, a national-conservative political party in France and one of its main political forces.
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A French politician who is the president of the National Front (FN), a national-conservative political party in France and one of its main political forces.
Ms Le Pen announced 144 “commitments” at the start of the two-day rally in Lyon. The proposals include leaving the eurozone, holding a referendum on EU membership, slapping taxes on imports and on the job contracts of foreigners, lowering the retirement age and increasing several welfare benefits while lowering income tax.
The manifesto also foresees reserving certain rights to French citizens only, including free education, hiring 15,000 police, curbing migration and leaving Nato’s integrated command.
“The aim of this programme is, first of all, to give France its freedom back and give the people a voice,” Ms Le Pen said while introducing her manifesto.
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