The 52-year-old prisoner was unconscious, put on ventilator and his overall condition was critical, a PGIMER spokesperson said here.
Sanaullah, who was brought to PGIMER from Jammu last evening, is being looked after by a team of neurosurgeons and other doctors at PGIMER's Intensive Care Unit.
Earlier, a medical bulletin said the prisoner's urine appeared to be adequate and "further treatment will depend on his stabilisation and neurological status".
A team of Pakistani High Commission officials visited Sanaullah at the PGIMER after India granted consular access to them last night.
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.