Four persons, all Pattali Makkal Katchi functionaries, were arrested on Thursday in connection with the attack on former Congress MLA U. Balaraman on Tuesday.
According to police sources, Mr. Balaraman was attacked by some persons who accused him of helping PMK founder S. Ramadoss's brother Seeni and others to join the Congress party.
The former MLA suffered a cut injury in his ear and was admitted to a private hospital.
While three persons involved in the attack were apprehended the same day, a special team formed to investigate the case arrested Gaja alias Gajendran, PMK North Chennai West district youth wing president, Baskar, PMK 14th ward secretary, Madan, PMK R.K. Nagar area secretary and Vaigai Saravanan, PMK harbour area secretary, on Thursday.
A motorcycle used to commit the offence was seized, the sources said.