The R&B star became ill last Friday and has not been in the show since, Jonnetta Patton, his manager, said Thursday.
"Usher has had an amazing time on Broadway and loved every minute of performing on stage with the entire cast of `Chicago,"' Patton said. "He expresses his sincere apologies to all of his fans who purchased tickets to see him in 'Chicago' this final week and appreciates all of their love and support."
The show has done boffo business since Usher, playing conniving lawyer Billy Flynn, joined the Bob Fosse-Kander and Ebb musical. Christopher McDonald takes over the role of Flynn on Oct. 15. Understudy Bernard Dotson has played Flynn during Usher's illness.
"Usher made a spectacular Broadway debut, bringing a great dedication, work ethic and his amazing talent to the show," said the show's producer, Barry Weissler. "We all hope that he might return at some point for the many fans that were unable to see his wonderful performance as Billy Flynn. Usher has found a new home on Broadway and is welcome back anytime."