The pressure on Jose Mourinho is set to increase after a poor performance by Real Madrid saw it come away from bottom side Osasuna with just a point in a scoreless draw Saturday.
It was a miserable night for Madrid, who was without the suspended Cristiano Ronaldo and Sergio Ramos, with Kaka sent off 19 minutes after coming on as a substitute, while Jose Maria Callejon had a goal disallowed for a borderline offside decision.
The result means Madrid is 15 points behind La Liga leader Barcelona, which plays Malaga on Sunday, and four behind neighbor Atletico.
Osasuna had the better of the second half and could have won, but its final ball continually let them down.
Ronaldo was suspended after picking up his fifth yellow card of the season last week, and his absence was keenly felt.
Mourinho acknowledged the strong performance of Casillas but would not guarantee the club captain will be in the starting side next week.
In our last two games, the team has played well defensively, and (Casillas) has been a part of that," Mourinho explained. "I liked how he played against Celta as well, rising to the occasion to give his team a boost. Nevertheless, it is still too early to tell if he will play against Valencia on Tuesday."
There was little of note in the opening stages with neither team creating any clear openings.
Osasuna's Damia's opening shot went wide, and it took until the 25th minute for Madrid to have an effort on goal, with Angel Di Maria firing past the post.
Madrid was finding it a struggle to get in behind the hosts' defense, and when Fabio Coentrao found himself unmarked on the left of the area, rather than provide a crisp pass to the onrushing Gonzalo Higuain, the defender headed the ball into the ground and the hosts cleared.
Callejon's back header narrowly cleared the bar for Madrid and as the half wore down, Osasuna midfielder Alvaro Cejudo blazed a half-volley high and wide.
Madrid failed to take advantage of a good chance in the final minute when Callejon set up Coentrao with the goalkeeper out of position but he fired wide.
The second half started much as the first ended with plenty of possession for Madrid but no clear openings.
Two quick-fire corners for Osasuna ended with Manuel Lolo heading over when he could have directed it across Casillas and into the far corner, but the hosts were enjoying a threatening spell, with Emiliano Armenteros forcing the goalkeeper to go down to his left.
The tempo of the game had risen considerably and Osasuna sensed it could take all three points, an outcome that appeared more possible when Madrid was reduced to 10 men.
Kaka had only been on the pitch for two minutes when he was booked and when he did not retreat so Osasuna could take a quick free kick, he was given a second yellow in the 77th minute.
However, it was Madrid that thought it had taken the lead moments later, but Callejon was judged to have been offside in a borderline decision.
Karim Benzema forced Fernandez to go down to collect his shot in Madrid's first shot on target in the second half but it was one of the last kicks of a miserable game for the visitors.
Roberto Soldado took his tally to 17 goals for the season as Valencia beat Sevilla 2-0 and continued its improvement since Ernesto Valverde replaced Mauricio Pellegrino as coach.
Los Che made it seven wins from eight games under Valverde to move up to seventh a point behind Malaga in the final Champions League spot in fourth. Sevilla remains 12th in the table following the loss.
Soldado netted from close range five minutes into the second half then wrapped up the win in the closing moments with a header from a Pablo Piatti corner to make it 11 La Liga goals for the season.
Patrick Ebert inspired Valladolid with two goals and an assist as it claimed its first win in five games over Mallorca with a 3-1 victory.
The German fired the hosts into the lead with a wonderful strike from 20 yards after 21 minutes but Mallorca was level before halftime as Victor rose to head home Javier Arizmendi's cross 16 minutes later.
Ebert proved the difference in the dying minutes as Oscar Gonzalez turned home his cross three minutes from time and the former Hertha Berlin man then went through on goal and jinked past Dudu Aouate before slotting into an empty net.
Sergio Garcia's first-half goal was enough to hand Espanyol a crucial three points as it moved out of the relegation zone with a 1-0 win over Celta Vigo.
The former Spanish international gave the hosts the perfect start as he tapped home Christian Stuani's cross from close range on 23 minutes, and despite having more of the ball after the break, Celta struggled to create clear-cut chances.
Information from Press Association was used in this report.