Eric Ciotti, a member of the centre-right Les Republicans, condemned the country’s new president-elect.
He said: “His overall ambiguity is what won him the election. All his proposals and vague. And now he’s trying to get top left- and right-wing officials to join his political movement, La Republic En Marche.
“He is trying to destroy Les Republicains.
Mr Ciotti told BFM TV: “He’s already destroyed the Socialist party, but he will not destroy us. Because we have a strong backbone and values.”
He added that, unlike the Socialist party, Les Republicans had not “imploded” when its official candidate, scandal-hit François Fillon, was eliminated in the first round of the presidential election on April 23.
Mr Ciotti confirmed that he had cast a blank vote in the French presidential election because he did not want Mr Macron to have “free rein” to do whatever he liked with the country, and because he did not think that his second-round opponent, far-right chief Marine Le Pen, “stood a chance of winning”.
Mr Ciotti went on to say that Mr Macron, 39, would struggle to distance himself from his former mentor, outgoing president François Hollande, and that his policies would be “more left- than right-wing”.
The young centrist famously quit as Mr Hollande’s Socialist economy minister in August 2016 to form his own political party and to join the presidential race.
He won the French presidential election with 66 per cent of the vote and will take office as France’s next president on May 14.