The injured Pakistani prisoner continues to be critical in hospital for the third straight day Sunday, officials said.
Sonaullah assaulted in an Indian-controlled Kashmir jail is undergoing treatment in the intensive care unit of Post Graduate Institute (PGI) of Medical Education and Research Hospital in Chandigarh city.
"He continues to be critically sick in deep coma almost in the same status as yesterday with no neurological improvement," reads a statement issued by Manju Wadwalkar, the public relations officer at PGI hospital.
Doctors at PGI hospital have put Sonaullah, 52, on a ventilator.
Sonaullah suffered multiple head injuries Friday morning after being attacked by another inmate inside the Kot Balwal jail of Indian-controlled Kashmir. The attack on Sonaullah was seen as an apparent retaliation to the death of a convicted Indian spy Sarabjit Singh on Thursday.
Singh was assaulted by a fellow prisoner inside a Lahore prison on April 26.
Sonaullah immediately slipped into comma after the attack and was initially taken to Government Medical College hospital in Jammu but later on airlifted to PGI hospital for specialized treatment.
Indian officials say there are 535 Indian prisoners in Pakistani jails and 272 Pakistani prisoners in Indian jails.
According to Syed Akbaruddin, the spokesman of India's Ministry of External Affairs, India was proposing a meeting of officials in both countries to "identify and put in place further measures to avoid such tragic incidents in future".