A case has been registered against four persons, including the brother, in connection with the incident, they said.
Police said the advocate Ravichandran suspected his brother's involvement in the attack as he had a property dispute with him.
Police said initial investigation revealed that hired gangsters had been engaged to attack the advocate.
The incident, which occurred at midnight yesterday, was captured on CCTV camera near the advocate's house, police said.
Ravichandran was returning home on his two-wheeler when unidentified persons who were following him on a two-wheeler attacked him.
He was first admitted to the government hospital here and later shifted to a private hospital.
As per the CCTV footage, two persons were seen attacking the advocate with a hockey stick while one person was seen hacking him with a sickle, police said.