The source, who is said to know Mac's family, said the comedian was in dangerously poor health while receiving treatment for pneumonia Saturday, the Chicago Sun-Times said Sunday.
The unconfirmed report came after the Chicago native's publicist, Danica Smith, denied multiple reports regarding the entertainer's alleged demise.
"It is a very horrible rumor," Smith said Saturday. "It is absolutely untrue. Nothing has changed from yesterday."
Initial reports regarding Mac's hospitalization were released Friday and Smith informed the media the "King of Comedy" star, whose real name is Bernard McCullough, was responding well to medical treatment.
The Sun-Times said Smith also confirmed McCullough's bout with pneumonia was unrelated to his diagnosed sarcoidosis, a chronic disease that has been in remission in "The Bernie Mac Show" star since 2005.
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