Sergio Ramos broke his nose during Real Madrid's 0-0 draw with Atletico Madrid on Saturday.
The rugged defender attempted a first-half header at goal in the Liga encounter, and was inadvertently kicked in the face by Atleti defender Lucas Hernandez.
The referee chose not to award a penalty, and Ramos subsequently had his nose plugged up by Real's physios, before being replaced by Nacho Fernandez at half-time.
And it has now been confirmed that the Real captain sustained a fracture of the nasal septum, though it remains to be seen if he will be out for any period of time.
Speaking afterwards Zidane said: "It is a fracture, for Sergio. I believe it's broken. I don't know how long he'll be out for."
Emilio Butragueno, Madrid's public relations director, told beIN Sports: "Ramos is going to have tests but if he has left the game it is a bad sign.
"We have to be careful and see what the doctors tell us."
Real face APOEL in the Champions League in midweek, before hosting Malaga in La Liga next weekend.