The prisoner is on ventilator and in deep coma, hospital sources said.
Sanaullah was airlifted from Jammu to the Post Graduate Institute of Medical Education and Research (PGIMER) on Friday evening.
52-year-old Sanaullah is being looked after by a team of doctors, including neurosurgeons, in the intensive care unit.
Early on Saturday a team of Pakistani High Commission officials visited Sanaullah, a resident of Sialkot in Pakistan. The officials are expected to meet the doctors again today to seek a fresh update on his condition.
In its medical bulletin last night the hospital authorities said that "the patient had metabolic alterations and coagulation abnormalities, which are being taken care of by concerned specialists and these are gradually being controlled, though they are not totally normal. His blood pressure had been going down, so a third vasopressor had to be added".
The hospital authorities said that Sanaullah was checked by neurosurgeons at the Jammu hospital, where he was first rushed to after the attack on him, and "detected head injuries with a large fracture. CT scan showed multiple contusions with severe brain edema (brain capillaries damaged due to head injury)."
Sanuallah is serving a life term after being convicted under TADA provisions following his arrest in 1999.
Two prison officials, including Jail Superintendent Rajni Sehgal, had been suspended by the Jammu and Kashmir government in connection with the assault.