The Spanish outfit were well worth their victory, being two goals to the good by half time.
Lucas Leiva got the Reds consolation with nine minutes remaining, but despite a late flurry Madrid held out.
"He's okay," Benitez told the club's official website.
"He twisted his ankle and it was just a precaution to bring him off because we have had problems with the other centre backs and we wanted to protect him."
Asked if it was a concern with Martin Skrtel and Daniel Agger already out injured, Benitez added: "We will have to wait now, the three players are injured, but improving so I think they will be fit for the next game."