Singh was lodged in Lahore Jail as a death row convict.
Sources say four of his family members from India will go to Pakistan on Sunday (April 28) to meet Singh, who is battling for his life in the hospital.
Sarabjit's lawyer, Awais Sheikh informed that his condition is critical. "He is in coma and is critical. 60 per cent of his brain is damaged... his backbone is broken," added Sheikh.
"Yes, it was an attempt to murder my father. It was all planned because in the morning we were hearing that the authorities of jail were saying that he has been attacked while shifting the barrack but now the authorities are saying that he's been attacked in his barrack only. We are unable to understand what they want to say. It shows that it was already planned and authorities were also involved," Swapandeep Kaur, daughter of Singh said.
Sarabjit, 49, was convicted for alleged involvement in a string of bomb attacks in Punjab province in Pakistan, that killed 14 people in 1990. His mercy petitions were rejected by the courts and former President Pervez Musharraf.
The Pakistan High Commission in Delhi has issued 15 days 'gratis visa' to Sarabjit's wife Sukhpreet Kaur, daughters Poonam, Swapandeep Kaur and his sister Dalbir Kaur to meet the Indian prisoner.
"We have got the visas and we will be crossing over to Pakistan tomorrow (Sunday) morning. Our (visa) papers will reach here (Amritsar) by the evening," Sarabjit's sister Dalbir Kaur.