Martin Schulz insisted Marine le Pen will not win the French election
Mr Schulz – the ex-European Parliament chief – claimed the possibility of Ms Le Pen storming to victory is "unthinkable".
He said: "She will never win, I'm absolutely sure."
The outspoken Europhile said he would even be willing to put a bet on Ms Le Pen failing to win the election.
She is widely tipped to reach the second and final round of the presidential vote, to be held in May.
But most pundits predict she will be beaten by Republican hopeful Francois Fillon or independent candidate Emmanuel Macron.
The Front National leader is expected to reach the final round of voting
Marion Le Pen in pictures
Wed, July 27, 2016
The niece of French far-right leader Marine Le Pen has joined the military reserve and has urged "young patriots" to follow in her footsteps, take a look through her career to date,
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French far right Front National (National Front – FN) party's Parliament member and candidate for the regional elections in the Provence-Alpes-Cote d'Azur (PACA)
Either it radically and deeply changes, or it will die
Marine le Pen
Speaking on the same documentary as Mr Schulz, Ms Le Pen warned the EU will break up unless it undergoes radical reforms.
She said: "Either it radically and deeply changes, and it abandons its authoritarian character, or it will die."
The MEP also branded the Euro a "political weapon".
Ms Le Pen claims the EU will 'die' if it is not radically reformed
She said: "The Euro is a knife which the EU puts into the backs of the people to force them to go where they don't want to go.
"Do you think we, France, will allow ourselves to be blackmailed, threatened? By whom? By people who are not elected?
"It's out of the question."
• After Brexit: The Battle for Europe will be broadcast tonight at 9pm