Sarabjit Singh in "deep coma", no surgery can be performed till condition stabilises, said official sources. "Doctors attending to Sarabjit Singh informed the Indian officials that he is in coma on ventilator and receiving IV drip," External Affairs Ministry spokesman Syed Akbaruddin said.
"The officials of India's High Commission in Islamabad obtain access to Sarabjit in the ICU of Jinnah hospital, Lahore at 2:00 am," he said.
Earlier, India has sought consular access to the 49-year-old Sarabjit.
The attack occurred when the victim and other prisoners were brought out of their cells for an hour-long break. The two prisoners assaulted Sarabjit with blunt objects and he sustained a severe head injury.
Sarabjit was initially taken to the hospital within the prison. After his condition worsened, he was moved in an ambulance to the state-run hospital, officials in Lahore said.
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.