The 22-year-old was carried off on a stretcher in the final moments of the routine victory, but was quick to reassure fans that it was not a serious problem.
"It was an isolated incident, I felt a pull in my leg," he told the club's official website.
"The doctor told me it would be best to go to the changing room. I hope it's nothing and I have a good feeling about it.
"I want anyone who is worried to relax, in two or three days I'll be fine."
Left-back Marcelo scored the second of Madrid's goals to send Carlo Ancelotti's side three points clear at the top of La Liga after Barcelona's 1-0 defeat at Real Valladolid on Saturday.
"We couldn't slip up today, so we focused more on the job at hand," he said.
"We can't count out Barcelona as they're a top side and we respect our rivals always.
"Now we have a week to rest a little bit and to continue trying to win every game."
