Sarabjit, 49, was in an Intensive Care Unit of the state-run Jinnah Hospital in Lahore, where he was admitted yesterday after being brutally beaten by at least six other prisoners within his barrack at the Kot Lakhpat Jail.
Official sources told PTI that Sarabjit was in a "deep coma" and doctors were unable to perform surgery on him yesterday because of extensive internal bleeding caused by a severe head injury.
"No surgery can be performed till his condition stabilises," a source said. The sources quoted doctors at Jinnah Hospital as saying that Sarabjit's condition was measured as 5 on the Glasgow Coma Scale (GCS), which indicates the level of damage or injury to a person's central nervous system.
The GCS comprises tests of eye, verbal and motor responses. The three separate values and their sum are considered in deciding a person's status.
The lowest possible GCS score is 3 while the highest is 15. Pakistani TV news channels quoted their sources as saying that next 24 hours would be crucial for Sarabjit.
Two Indian High Commission officials got consular access to Sarabjit Singh in the ICU of Jinnah Hospital this morning.
"The officials of India's High Commission in Islamabad obtained access to Sarabjit in the ICU of Jinnah hospital, Lahore at 2:00 am," External Affairs Ministry spokesman Syed Akbaruddin said.
"Doctors attending to Sarabjit Singh informed the Indian officials that he is in coma on ventilator and receiving IV drip," he said.
The Indian mission had contacted Pakistan's Foreign Office last night to seek consular access. The two Indian officials went to the hospital and spent some time with Sarabjit.
They then drove away from the hospital without speaking to the media. Security has been beefed up at the hospital, where dozens of police commandos have been deployed.
Indian High Commission officials were in regular contact with the Medical Board attending to Sarabjit. Even as Sarabjit was in coma, doctors carried out X-rays, MRI, CT scans on him.
Doctors have been carrying out trauma control and await stabilisation in condition before conducting further tests, Akbaruddin said.
Some news channels reported that a team of Indian doctors might visit Lahore to assist in Sarabjit's treatment though this could not be independently confirmed.
Earlier, sources told PTI that Sarabjit was attacked by at least six other prisoners within his barrack in one of the most secure sections of Kot Lakhpat Jail.
He was hit on the head with bricks and his face, neck, and torso were cut with blade and pieces of a ghee tin.
Sarabjit was initially taken to the hospital within the prison. When his condition worsened, he was moved in an ambulance to Jinnah Hospital.
However, a murder case has been registered against two prisoners Amer Aftab and Mudassar.
Sources said Aftab, who was on death row after being convicted of murder, had quarrelled with Sarabjit and attempted to attack him some days ago.
Sarabjit was convicted for alleged involvement in a string of bomb attacks in Punjab province that killed 14 people in 1990.
His mercy petitions were rejected by the courts and former President Pervez Musharraf.
The outgoing Pakistan Peoples Party-led government put off Sarabjit's execution for an indefinite period in 2008.
Sarabjit's family says he is the victim of mistaken identity and had inadvertently strayed across the border in an inebriated state.