Fresh from inspiring Portugal to FIFA World Cup qualification with a phenomenal midweek hat-trick against Sweden, Ronaldo netted the 25th goal of an already remarkable club campaign when he converted Isco's third-minute cross.
He walked off gingerly early in the second period after being second best in a tackle with Aleix Vidal, but Madrid's medical team later confirmed the problem as a dead leg, according to Spanish newspaper AS, and the player himself insisted there are no major concerns.
The forward told radio show Carrusel Deportivo: "It's a knock. It's nothing serious."
Real Madrid manager Carlo Ancelotti added in his press conference: "I don't think it's serious, because he's not in any pain.
"Tomorrow (Saturday) we will do a medical check but (it is) not a major problem."
Real did not feel the impact of their talisman's withdrawal too keenly as Karim Benzema, Gareth Bale, Isco and Alvaro Morata completed the rout.
Ancelotti hailed a complete team performance, reserving praise for the performances of Xabi Alonso and Asier Illarramendi at the base of a re-shaped midfield in the absence of long-term knee injury victim Sami Khedira.
"Everyone did a good game,” he added. "We did not concede a goal. That is important and the whole team played well, worked well.
"Illarra and Xabi played well and the team has had more balance."
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