Xavi admits the benefits of a victory for his side would be huge, but insists the Catalan giants are not getting carried away with the situation.
He said today: "It would be a seventh successive victory in the league for us and a big blow to morale for Madrid.
"It would a very important advantage but we could still lose those points.
"Whatever happens there is still a lot of the season left. A win would give us a lot of confidence because it's our age-old rivals, and would make the league more difficult for them. They are three very important points but the league will not be decided in this match."
The Spain international added: "Regardless of the points difference anything can happen. This is Madrid. Last year we were also favourites and they won here."