Casillas is match-fit after breaking a bone in his left hand in the quarterfinal of the Cop del Rey in Valencia in January and has made a rapid recovery, Xinhua reports.
However, as a result of his injury the club signed Diego Lopez from Sevilla to provide cover and Lopez, who spent several years as Casillas' understudy before joining Villarreal, has performed well in Casillas' absence and produced a memorable performance in Real Madrid' s Champions League tie in Old Trafford last month.
Whoever plays Saturday is almost certain to be in goal for the first leg of Real Madrid's Champions League game at home to Galatasaray Wednesday, therefore Jose Mourinho's decision is more important than it may first appear.
Will Mourinho be willing to take a risk on playing Casillas, even though he has proved his fitness in training? Or will he maintain faith in a goalkeeper, who so far has done nothing wrong?
There is another factor at play given that the relationship between Mourinho and Casillas is thought to be strained with Casillas having been dropped for a couple of matches before his injury and his journalist girlfriend Sara Carbonaro having commented on Mexican TV that some players and the coach don't see eye to eye.
If Mourinho wanted to show Casillas a lesson, this would be the moment to do so and whoever plays is likely to provoke debate in the press and on the stands.
Zaragoza go into the game with the worst record in Spain in 2013 and have not won since their last game of 2012. That run of form has seen them slip to fourth from bottom of the table and they are currently staring at a drop into the relegation zone, especially as Mallorca have begun to pick up points in recent weeks.
Not only are they out of form but Manolo Jimenez's side have the worst home record in the league with just three home wins and three draws from 13 games.
Jimenez will be hoping that Mourinho approaches the game with one eye on the Champions League, which is clearly Madrid's big obsession for the rest of the season.
That obsession will see Madrid rest some players likely to start Wednesday with Angel di Maria and Gonzalo Higuain likely to be rested after playing in Bolivia Tuesday.
Cristiano Ronaldo could also be on the bench, although he could play after being suspended in midweek, while Xabi Alonso and Sami Khedira could also sit the game out.
That would see Pepe push into midfield with Kaka, Javier Callejon and perhaps Alvaro Morata all in the starting 11 along with Raul Albiol.
Sides struggling alongside Zaragoza to avoid relegation may not be pleased to see Mourinho field anything less than his strongest team, but Mourinho's eye is on the Champions League and Zaragoza for one are not complaining.
--IANS (Posted on 29-03-2013)