Mohammed al-Qiq's health is "very, very bad," lawyer Jawad Boulus told AFP after a visit on Sunday. "He faces the possibility of death at any moment."
Qiq, a 33-year-old father of two and a correspondent for Saudi Arabia's Almajd TV network, was arrested on November 21 at his home in the West Bank city of Ramallah and is being held under Israel's controversial administrative detention law.
He has been refusing food since November 25 in protest at "torture and ill treatment that he was subjected to during interrogation", according to Addameer, a Palestinian human rights organisation.
Shin Bet, the Israeli domestic security service, alleges Qiq is an active member of the Islamist group Hamas which controls the Gaza Strip.
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Administrative detention laws allow Israel to jail suspects without trial for six-month renewable periods, a policy which has been condemned by human rights advocates.
Qiq was transferred to hospital in the Israeli city of Afula about a month ago, a prisons authority spokeswoman said.
His family have previously said they expect Israel to feed him intravenously if he loses conciousness, though Israeli authorities have denied they will force-feed him.
Top Palestinian official Saeb Erekat told AFP that Israeli Prime Minister Benjamin Netanyahu "personally bears responsibility for Al-Qiq's life".
Qiq was jailed for a month in 2003 and then for 13 months in 2004.
In 2008, he was sentenced to 16 months on charges linked to his activities on the student council at the West Bank's Birzeit University.
Mohammed Allan, a 31-year-old prisoner, ended a two-month hunger strike in August 2015 after his detention was suspended.