The gang took to their heels after the local villagers rushed to save the driver.
Police said eight of them had been arrested and that the motive for the attack was not immediately clear. Karthikeyan was returning home after worshipping at a temple.
The driver was treated at the government general hospital.
Karthikeyan had unsuccessfuly contested the May 16 assembly polls as an independent after being denied a ticket by his party to retain Oussudu reserved constituency.