A Palestinian prisoner on his 61st day of hunger strike while shackled to a bed in an Israeli hospital is in immediate danger of death, according to a medical report submitted to the supreme court in an effort to secure his release.

Khader Adnan, 33, a baker from a village near Jenin, is being held without charge by the Israeli authorities under a four-month term of "administrative detention". He began his hunger strike on 18 December, the day after being arrested.

Adnan's lawyers have submitted a petition for his release to Israel's supreme court, but no date has been set for a hearing. The situation was urgent, lawyer Mahmoud Kassandra told the Guardian. "This is the last chance. The medical report says he could die at any minute. We hope this will succeed but I am not optimistic."

Adnan's hunger strike is in protest at his detention without charge or being told of any evidence against him, and over his claims of abuse and degrading treatment during arrest and interrogation. This is his ninth period of detention, according to reports. In the past he has acted as a spokesman for the militant group Islamic Jihad.

He was examined by a doctor from Physicians for Human Rights on Wednesday at the Rebecca Ziv hospital in Safed. Adnan was shackled by both legs and one arm, the doctor reported.

"He has lost 30kg and weighs 60kg. He suffers from stomach aches, vomiting, sometimes with blood, and headaches … His general condition is pale and very weak, his tongue is smooth, he has slight bleeding from the gums, dry skin, loss of hair, and significant muscular atrophy. His pulse is weak, blood pressure 100/75. He is permanently connected to a heart monitor."

Adnan agreed to be treated with an infusion of liquids and salts, with the addition of glucose and vitamins, the doctor reported. "However, he maintains his refusal to end his hunger strike." He was lucid and aware.

He was "in immediate danger of death," the doctor concluded. "An absolute hunger strike in excess of 50 days causes the decomposition of muscles... and the creation of toxins in the body. Death may occur suddenly, due to heart failure or the result of infection following the collapse of the immune system. Bleeding in the digestive tracts and renal or hepatic failure are possible.

"A fast in excess of 70 days does not permit survival. Infusion of liquids, adjustment of salts, and the addition of glucose and vitamin cannot prevent certain death due to such a protracted hunger strike."

Adnan's wife, Randa, his two daughters and his father were permitted to visit him on Wednesday, although his mother, sister and brother were refused.

"Randa told me he was very thin and his health was worsening but his mental health is good," his sister Maali said from the family home in Arrada. "But the whole family is worried, and Randa doesn't know if she will see him again."

Adnan's elder daughter, also called Maali, who is nearly four, understood her father is very sick and was anxious about giving him a hug, the older Maali said. "She is telling her mother, please stop crying." The younger daugher, Bissan, is 18 months and Randa is six months pregnant with the couple's third child.

Following the visit, Adnan's father addressed a demonstration outside the hospital in solidarity with Adnan, reporting that his son's morale was high. "He does not undertake this hunger strike for its own sake, but he yearns for freedom for his people, for his countrymen, in order to live with heads held up high, without occupation," Jihad Adnan told protesters.

Thousands of Palestinians and other supporters of Adnan have protested in the West Bank and Gaza, and outside Ofer military prison near Jerusalem. There have been clashes with police, who have fired tear gas and rubber bullets.

According to Addameer, a Palestinian prisoners' support group, detainees in other prisons have also begun refusing food.

Many protesters say Adnan has become a symbol of Israel's occupation and its treatment of prisoners. More than 300 Palestinians are held under "administrative detention" orders in Israeli prisons.

The Palestinian Authority has appealed for Adnan's release. Physicians for Human Rights on Thursday urged to Israel's president, Shimon Peres, to intervene in the case because of the prisoner's dire medical condition.

Earlier this week, an Israeli military court rejected an appeal against Adnan's continued detention. The Israeli prison service has said Adnan was being dealt with in accordance to his "definition as a security-administrative prisoner" and with humanitarian sensitivity.

Adnan's hunger strike has attracted a big following on Twitter and Facebook. Many of his supporters complain his case is being ignored by the mainstream media. There has been little coverage in the Israeli and international press.

Bobby Sands, the Irish republican prisoner who died on hunger strike in a Northern Ireland prison in 1981, lasted 66 days without food. According to the British Medical Association, death generally occurs between 55 and 75 days of a hunger strike.