World Bulletin / News Desk
Conservative politician Nathalie Kosciusko-Morizet was handing out campaign flyers at a market ahead of Sunday's legislative election run-off.
Her campaign team said she lost consciousness briefly and was taken to hospital.
Paris prosecutor's office has opened an investigation into an act of "deliberate violence". No suspect has yet been arrested.
French Prime Minister Edouard Philippe visited the Republicains lawmaker in hospital and tweeted a message of support.
Footage broadcast by BFMTV shows a man throwing leaflets in the face of the former presidential primary candidate, as she tries to protect her face with her hand.
More footage shows her unconscious on the pavement with passers-by checking on her.
The man reportedly approached Kosciusko-Morizet, yelled insults then ran away after he knocked her to the ground near a metro station.
Kosciusko-Morizet, 44, a former environment minister and spokeswoman under ex-President Nicolas Sarkozy, was defeated by Socialist Anne Hidalgo in her bid to become the first female mayor of Paris in 2014.
She is campaigning to win a seat in her central Paris constituency against Gilles Le Gendre from President Emmanuel Macron's LREM movement.
Several French politicians, including Le Gendre, took to Twitter to condemn the attack.