French media quoted witnesses as saying that a man insulted Ms Kosciusko-Morizet and pushed campaign leaflets into her face.
Pointing his finger in the politician's face, he said she was a "dirty bobo" - the French word for a young aspiring professional with liberal views, or yuppie as they are often called in the United Kingdom and USA.
The man in his 50s called her a "crappy bobo", a derisive term for an urban hipster, AFP said.
She lost her balance and after falling, she blacked out for several minutes possibly after hitting her head, before being revived by emergency services.
A leading female French politician was knocked unconscious by a vicious thug who launched a "cowardly and intolerable assault" as she handed out leaflets in a market.
NKM, who lost out to François Fillon in last year's right-wing presidential primary, was reportedly treated at the scene by paramedics before being taken to hospital. He also yelled "go back to l'Essonne", the department near Paris for which she is now an MP. "I condemn this unbearably violent act", he said in a tweet.
NKM, 44, a former environment minister in Nicolas Sarkozy's centre-right government, hopes to be elected in the second round of France's legislative elections on Sunday.
An official inquiry for "deliberate violence" has been opened into the incident, which happened at a market in Paris's chic 5th arrondisssement.
She faces a battle to win a seat against Gilles Le Gendre from the Republic on the Move party (En Marche!) of Macron.
Le Gendre later announced he was suspending his campaign because of what had happened to his opponent.