The Brazilian star will miss the Bernabeu encounter as he serves the second game of a three-match suspension for sarcastically applauding his red card against Malaga.
Rakitic told Sky Sports News: "I don't think it needs repeating that [Neymar] is an important player. [The suspension] is not good, but it is what it is. We need to understand the situation and push on.
"In the past we have already shown that we can also win when Neymar isn't playing. Of course, it would be much better to have him with us, because he is one of the two or three best players in the world.
"We have a lot of confidence and we have a very strong team. We want to show Neymar that when he is not with us we can still do it, and hopefully we can take a victory for him."
Barcelona go into Sunday's El Clasico three points behind La Liga leaders Real, having played a game more.