Valencia winger Nani has suffered an injury to his left thigh, the LaLiga club have confirmed.
The Portugal international was substituted six minutes before half-time during Wednesday's impressive 2-1 win over Real Madrid at the Mestalla.
In a statement on their official website, Los Che said the 30-year-old had sustained "a muscular injury in his left thigh".
Valencia will assess Nani's condition over the coming days and are yet to put a timescale on his absence.
Nani has three goals in 19 appearances since moving to Spain's top flight from Fenerbahce during Portugal's triumphant Euro 2016 campaign.
Voro Gonzalez's side travel to Copa del Rey finalists Alaves in LaLiga on Saturday.