Mane, who owns a footwear shop in Talegaon-Dabhade, some 40 km from here, was attacked soon after he opened the shop.
"Mane said the attacker threatened to kill him before hitting him," Police Inspector Sanjay Nikam told IANS.
"He is still undergoing some medical tests and is not fit to speak," he added. Mane worked closely with another RTI activist Satish Shetty who was killed in January 2010. Like Shetty, Mane had also asked for police protection.
In 2010, six activists were killed and several assaulted in Maharashtra, says a report by Mumbai-based NGO Movement against Intimidation, Threats and revenge against Activists.