Gerardo Martino's men will head to the Bernabeu four points behind Madrid in the title race, and knowing they cannot afford to cede any more ground as the season moves into the final stretch.
But although they are still in the thick of the battle, and also through to the quarter-finals of the Champions League, there are murmurs of discontent around the club and Andres Iniesta has admitted he is at a loss as to why some fans are questioning Barca's direction.
"We have to have confidence in ourselves, as we always have with this kind of game. We aren't 20 points behind the leader and there's no big difference in results or the way we are both playing," he said.
"It's hard to believe there are Barca fans who don't believe in us. This team has won the right to the fans' trust - sure we've had off days, but nobody should think Madrid are going to find us an easy prospect."
While Barca cannot afford defeat, Atletico Madrid may well be rooting for a draw as they seek to become the first side other than Madrid or Barca to take the title since Valencia in 2004.
By the time the big match kicks off, Atletico will already have played their match away to rock-bottom Real Betis, where victory would put them level on points with their city rivals, at least for a few hours.
Although El Clasico has a habit of overshadowing all else in Spain, Gabi has told his Atletico team-mates to worry only about their own game against a side nursing emotional wounds following their Europa League exit at the hands of arch-rivals Sevilla on Thursday night.
"Betis are worthy of being considered a big team," Gabi said. "They are a team who need to take their chances in the league and on Sunday they have another. But if we can win in Seville, any result in El Clasico can work for us."
Although the manner of their defeat - in a penalty shoot-out - will sting for Betis, their exit from European competition will at least focus minds on the huge challenge of saving their season as they sit nine points adrift of safety.
They are seven points adrift even of 19th place, which currently belongs to Almeria ahead of their match against Real Sociedad on Monday night.
Real Valladolid, 18th, face Rayo Vallecano on Saturday, and a win for the hosts would shake up a close relegation battle, with the six sides immediately above the bottom three all nervously looking over their shoulders.
Getafe face a tough trip to fourth-placed Athletic Bilbao with only a two-point cushion over the drop zone, while Malaga, Osasuna and Rayo Vallecano are just one point better off.
Malaga get the first shot at improving their lot away to Celta Vigo on Friday night, while Rayo Vallecano are away to Real Valladolid on Saturday and Osasuna host Sevilla on Sunday.
Also on Sunday, Europa League quarter-finalists Valencia take on Villarreal, while Granada host Elche and Levante travel to Espanyol in Saturday's remaining fixtures.