The elder Culkin, 69, fell ill at his home in Grants Pass Tuesday afternoon.
He was admitted to a hospital where it was determined he had lost nearly all motor function. The prognosis for his recovery is not good, the celebrity news website said.
Macaulay Culkin, who starred in the classic "Home Alone" and film comedies in the 1990s, has been estranged from his father for years.
Kit Culkin, a former actor, worked as manager of his sons' careers before splitting up with their mother Patricia Brentrup in 1995. He is the brother of "Parenthood" actress Bonnie Bedelia.