Los Blancos recorded a 3-1 win over Paris Saint-Germain in the first leg of their last-16 tie on Wednesday night.
The result has made the European champions the strong favourites to progress into the final eight, but Navas has said that "nothing is won yet" as the Spanish giants prepare for a tough return match in Paris.
"We hold an advantage but nothing is won yet and in Paris it will be dangerous," Marca quotes Navas as saying. "The first leg brought a very good result for us so it is natural that right now we are happy, but now we must focus on how we can advance from this position.
"The Champions League is a competition which motivates us and sometimes that is difficult to explain."