Real are trying to win the Champions League for a third successive season. They meet Liverpool in the final in Kiev, Ukraine on 26 May.
"He's not great right now but I think it's going to be a small thing - it was only a bad movement," added Zidane.
"I can't say how long he'll be out for. Tomorrow he'll have a scan."
Ronaldo scored his 25th league goal of the season in the game against Barcelona.
Real are third in La Liga, 15 points behind champions Barcelona. Zidane's side have three more league games before they meet Liverpool in a repeat of the1981 European Cup final