This was announced on Sunday by Salzburg Festival's management.
Domingo was suffering from a bladder infection as well as a respiratory infection with high fever. He will be replaced by Polish baritone Artur Rucinski.
Domingo appeared as guest soloist with the Vienna Philharmonic Orchestra (July 23) under the baton of Daniel Barenboim at the Salzburg Festival. In a sold-out run of "Il Trovatore" (from August 9 on) he sang opposite Anna Netrebko.