Casillas concedes Real are struggling to rediscover last season's form.
He said: "Things are not going as well as last season. It's the same team, but it is not being reflected in the results like last season. We have perhaps lost a little of the respect that we earned ourselves on the pitch. We also have to fight and fight like them. It is not easy to grasp that there is such a big gap between us and the leaders.
"There are lots of points, it's December and the first half of the season has not finished. It hurts. We have a big squad that is well balanced and we have good players. We have to please the fans who came to the Bernabéu, who want to see their team win and to go home happy."