A spokesman said the R&B singer is suffering complications from throat surgery.
Kelly's publicist said in a statement that the singer was on his way to New York on Wednesday morning when he became ill and returned to Chicago for medical treatment.
Kelly had surgery last year to treat an abscess on his vocal cords. Kelly's new album, "Write Me Back," came out Tuesday and his memoir, "Soulacoaster: The Diary of Me," arrives Thursday.
The Grammy winner's publicist says Kelly will have to cancel appearances on "The Jimmy Fallon Show," NBC's "Today" and a book party. Kelly's spokesman says it's unclear how long the singer will be sidelined.