The militants raided Patharigaon village in the Jengrai area of the world's largest river island early this morning and shot at Dipankar Bora, alias Dipak Kachari, Jorhat Superintendent of Police Amanjeet Kaur said.
The injured was initially admitted to a local health centre from where he was shifted to Guwahati Medical College Hospital in a critical condition.
Bora was arrested two months ago on the charge of extortion and released recently from jail.
An investigation was on to ascertain the cause of the shooting. Bora would be interrogated after his condition stabilised, Kaur said.