Real are currently leading Barcelona in the standings.
"We have two games before the Clasico; the first against Athletic and then against Ajax (in the Champions League)," Butragueno is quoted as saying by Madrid's official website. "The Ajax match isn't decisive but it is important if we want to finish top of the group.
"Being top heading into the Camp Nou can be encouraging. The league will not be over after the Barcelona match, although last year the two games nearly decided La Liga. We must be aware of the smallest of details."
"The two teams are among the best in the world and I think they are also the two favorites to win the Champions League.
He added, "The team must continue improving because there is tremendous potential and I am sure Mourinho can bring out the best in each player.
"Every match is an opportunity for growth and maturation."