The defending Spanish champions welcome their arch rivals to the capital sitting 11 points adrift of the summit, having stuttered in the first half of the campaign.
Madrid, who also have a game in hand still to play, go into their final outing of 2017 knowing that anything less than victory will surely end their hopes of back-to-back titles.
Long-serving skipper Ramos has admitted as much, although he believes that he and his teammates now have some momentum on their side following success in the Club World Cup last week.
"It will be a great match," he told reporters. "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."
Madrid head into the match unbeaten in 10 in all competitions, including a run of four successive wins.