Los Blancos find themselves fourth in the standings, 11 points behind Barca (albeit with a game in hand) ahead of the match at the Santiago Bernabeu.
“It will be a great match,” Ramos said on Tuesday. “There are no words to describe the Clasico. It is totally different, and the most important game in the world.
“We are obliged to win now more than ever due to the situation we find ourselves in, in order to remain in the fight for La Liga.
“We come into it in good form after winning the Club World Cup, which always suits the team on a psychological level.
“We are eager to play and have been working hard this week, so hopefully we can get the three points that will allow us to stay close to those teams ahead of us.”
Barca claimed Clasico bragging rights last season with a 1-1 draw at the Nou Camp before beating Madrid 3-2 at the Bernabeu.
They have faced each other three times since then in less competitive circumstances, with Barca beating Madrid 3-2 in the International Champions Cup before Madrid won the Spanish Super Cup 5-1 on aggregate over two legs.