The bodyguard-turned-film-star was 54. His credits include "The Green Mile," "Armageddon," "The Whole Nine Yards," "Brother Bear" and "Sin City."
"Manigault is grateful for all of your prayers and asks for privacy at this time," a representative for reality TV personality Manigault said in a statement People.com. "Celebrations of his life, both private and public, will be announced at a later date."
"I am terribly saddened at the loss of Big Mike," People.com quoted Tom Hanks, Duncan's "Green Mile" co-star, as saying Monday. "He was the treasure we all discovered on the set of 'The Green Mile.' He was magic. He was a big love of man and his passing leaves us stunned."
Duncan, who was 6-foot-5 and 300 pounds, went into full cardiac arrest July 13, but was revived when Manigault performed CPR on him and transported him to a hospital where he was treated until Monday when he died.
The exact cause of his death was not immediately reported.
2014: The Year in Music [PHOTOS]