Metropolitan Opera soprano Jennifer Rowley will replace Yoncheva. In a Met La Bohème in 2014, Rowley "made a splash in her house debut as Musetta, maneuvering flirtatiously through the crowds and singing with a vibrant, agile voice," wrote a New York Times critic. She performed Tosca at the Met recently, and is slated to do so again in 2019.
The appearance by Yoncheva, much praised for her powerful, crystalline sound, was hailed as one of the high points in the orchestra's season, and was to have marked her Philadelphia Orchestra debut. "I finally got the Tosca that I've been dreaming about," conductor Yannick Nézet-Séguin said in February 2016, when the season was announced. "It's a Puccini opera that I have not so far conducted complete."
Yoncheva's recent illness has led to cancellations elsewhere. The orchestra's semi-staged production of Tosca is set for May 12, 16, and 19 at the Kimmel Center.