Ramos was forced off at half time.
The substitution was likely made as more of a precaution, but there will be an anxious wait as Ramos goes for further tests to determine if there is an issue there.
Real coach Zinedine Zidane said afterwards: "Let's hope it's nothing major, it's a knock and we'll do what we have to do tomorrow to see exactly what the issue is. Let's hope it's a minor one."
Real meet Barcelona later this week.