Barcelona maintained their two-point lead at the top on Tuesday after crushing Getafe 6-0 at the Nou Camp with Real responding the following evening with a 3-0 home victory over Almeria.
Four games remain for each side and Real appear to have the tougher task on paper with trips to Sevilla and Espanyol and home games against Valencia and Getafe.
Real visit Champions League-chasing Sevilla on Saturday evening just hours after Barcelona travel to bottom club Cordoba – and captain Casillas admits heading to the Estadio Ramon Sanchez Pizjuan is not an ideal fixture.
“It will be very tough, just as all our remaining fixtures will be,” Spain goalkeeper Casillas told Spanish reporters.
“They are a very strong side at home and have been solid throughout the season. They are also fighting for a Champions League place and are through to the semi-finals of the Europa League.
“It will be a fantastic game for the neutrals, but there are three vital points up for grabs as we need to win all our games and hope that Barcelona slip up.”
Barcelona are unbeaten in 15 matches, 14 of which they have won, and Cordoba will be relegated if they fail to win at Estadio Nuevo Arcangel on Saturday afternoon.
The omens are not good for Real as Cordoba have won only three league matches all season and their last victory came 16 games ago at Rayo Vallecano on January 12.
But Casillas said: “We want to make it difficult for Barcelona by picking up three hugely important points in our bid to win La Liga.
“We need to continue winning and wait for Barcelona to make a mistake. Cordoba, like Sevilla, also have a lot to play for.”
Defenders Sergio Ramos and Dani Carvajal are both available after suspension and Gareth Bale, who returned to training on Thursday, could return in attack after missing the last three games with a calf injury.
Fifth-placed Sevilla present a formidable test as they are unbeaten in 15 games and have not lost at the Sanchez Pizjuan in La Liga since February 2014.
The Rojiblancos are also the only side not to taste defeat against Barcelona since February having held the league leaders to a 2-2 draw last month.
Sevilla won 3-1 at Eibar on Wednesday to move level on points with Valencia in the race for the final Champions League place and coach Unai Emery says his team face an exciting finale with a Europa League semi-final to look forward to as well.
“The greatest satisfaction is the group. Everyone wants to write their name in Sevilla history,” Emery said after the midweek victory.
“We have open objectives in the league and one very clear objective in the Europa League. Every game is special.
“We will enjoy Saturday. We know it will be difficult to win (against Madrid) but we will try to do it.”