Lionel Richie's daughter checked herself into Los Angeles' Cedars-Sinai Medical Center after developing symptoms for the illness.
But fans have been warned not to worry - she is responding well to medical treatment.
Her representative tells UsMagazine.com, "Nicole has checked into Cedars-Sinai where she is being treated for pneumonia. She is doing well."
Richie gave birth to her second child, son Sparrow with boyfriend Joel Madden, in September (09).