Mamata Banerjee alleged that she was attacked during her campaign in Nandigram.
A case was registered on Thursday over the attack on West Bengal Chief Minister Mamata Banerjee, following a complaint lodged by TMC leader Sheikh Sufian, police said.
The case was lodged under IPC sections 341 (punishment for wrongful restraint) and 323 (punishment for voluntarily causing hurt), a senior police officer of the Purba Medinipur district said.
"We have received a complaint from Mr Sufiyan. Our investigation is already underway and we are collecting evidence," the officer said.
In the morning, District Magistrate Vibhu Goel, Superintendent of Police Praween Prakash and other officers visited the Birulia Bazar area where the incident happened.
The officers spoke to eye-witnesses, besides looking for any CCTV installed in the area to ascertain the exact sequence of events.
The chief minister is at present undergoing treatment at the SSKM Hospital in Kolkata with injury to her left leg, waist, shoulder and neck, according to doctors.
Ms Banerjee alleged on Wednesday evening that during her campaign in Nandigram, she was attacked by four-five men who pushed her, besides banging on her the door of her car, leading to the injuries.