The Santiago Bernabeu side will be without the experienced midfielder for up to three months due to a fractured metatarsal
The Spain international sustained a fractured metatarsal during Wednesday morning's training session and could be out of action for an estimated three months.
"Radiological tests performed by Real Madrid's medical services have revealed that Xabi Alonso has suffered a fracture of the fifth metatarsal of his right foot on Wednesday," a statement on the official Madrid website reads.
The 31-year-old only recently returned to full match fitness after missing Spain's Confederations Cup campaign due to a groin problem.
The news is a bitter blow to Carlo Ancelotti's plans as new signing Asier Illarramendi - dubbed the long-term replacement to Alonso at the heart of the Blancos midfield - is still short of match fitness following a muscular injury picked up in preseason.