The 2012-13 La Liga season is only a little more than a month old, but a loss on Sunday to rival Barcelona would likely end Real Madrid's chances to repeat as Spanish champions.
Barcelona are at the top of the league table with 18 points, and they already have an eight-point lead on Madrid. If Los Blancos were to suffer their third defeat of the league season, or even draw, it would be quite difficult for Jose Mourinho's men to prevent their rival from capturing another league championship.
Madrid has won their last four matches, so the team won't be lacking confidence going into the Nou Camp for a high-pressure showdown with Barcelona.
For Madrid to earn a much-needed three points, star forward Cristiano Ronaldo has to continue his spectacular play versus Barcelona.
Ronaldo scored three goals in Madrid's dominating win over Ajax in midweek, but the key for the club's attack might be the play of star striker Karim Benzema.
The French striker scored a wonder-goal versus Ajax on Wednesday, and he has played well versus the Catalan club over the last year.
Benzema will likely have an easier time than normal against the Barcelona defense because star center-back Carles Puyol will miss the match after picking up a scary arm injury in Tuesday's Champions League match versus Benfica.
His center-back partner, Gerard Pique, missed the Benfica clash with an injury, but may return for Sunday's El Clasico.
As important as Messi will be in this match, the most important goal for Barcelona will be to defend well, because Madrid can score two or three goals in a matter of minutes with the attacking firepower in their squad.
After losing the Spanish Super Cup to Madrid in August and having a chance to ruin their rival's league title hopes, Barcelona will be extremely motivated to dominate Madrid at the Nou Camp on Sunday afternoon.
Regardless of the outcome, this is guaranteed to be a great match with plenty of emotion, so let's look at the information you need to experience El Clasico.
When: Sunday, October 7 at 1:50 p.m. ET
Watch: Sky Sports 1 HD
Live Stream: Sky Sports
Where: Nou Camp, Barcelona, Spain