Taliban spokesman Zabihullah Mujahid released a statement on Monday saying that Kevin King is suffering from heart and kidney problems, and often loses consciousness.
Mujahid also says the Taliban will hold the U.S. government responsible if anything happens to King.
In August 2016, American Kevin King, 60, and Australian Timothy Weeks, 48, teachers with the American University of Afghanistan in Kabul, were kidnapped at gunpoint near the campus.
Since then, the Taliban have released two videos of the captives.
The Taliban wants freedom for its “soldiers” being held at the U.S.-run Bagram air base and the Afghan prison called Pul-e-Charkhi in return for freeing the two professors, the hostages said in their video message.
“My captors treat me well. They treat me and my colleague Tim Weeks as their guests; but every prisoner’s final wish is to get freedom from the prison,” said King, who was seen with a long beard.