John Singleton's family have said the Oscar-nominated director is in intensive care after suffering a stroke.
The filmmaker, known for movies including Boyz n The Hood, Shaft and 2 Fast 2 Furious, fell ill on Wednesday.
He is now in hospital "under great medical care".
The statement said: "On Wednesday, April 17th our beloved son/father, John Singleton, suffered a stroke while at the hospital.
"John is currently in the ICU and under great medical care.
"We ask that privacy be given to him and our family at this time and appreciate all of the prayers that have been pouring in from his fans, friends and colleagues."
Following news of the stroke, friends and colleagues sent their best wishes.
Rapper Snoop Dogg shared a picture of the pair together on Instagram, writing: "Pray 4 my brother."
Brian Koppelman, the co-creator of Billions, a TV drama Singleton has directed episodes of, said working with him had been a "career highlight".
Chicago Fire co-creator Derek Haas said: "John Singleton is a wonderful human. Get well!"
Actress Nia Long wrote: "Praying hard this morning for my friend @johnsingleton PULL THROUGH BABY."
Los Angeles-born Singleton's films often deal with themes of inner-city violence.
His 1991 film Boyz n The Hood earned him an Academy Award nomination for best director.
This made him the first African American nominee and the youngest ever.