The Lilywhites have been frantically searching for another goalkeeper since on-loan Chelsea goalkeeper Jamal Blackman broke his tibia in November, leaving Bailey Peacock-Farrell as their lone shot-stopper.
And The Yorkshire Evening Post say they have finally found their man and that Casilla will fly to England for a medical early next week.
The 32-year-old Spanish goalkeeper has fallen down the pecking order at the Bernabeu since Thibaut Courtois arrived from Chelsea last summer and has yet to feature this season.
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And he is now said to be ready to move on for the good of his career. It is believed Casilla could be signed at the beginning of next week.
Leeds were also keen on Fulham's Fabri and Newcastle's Karl Darlow but no agreement was reached on a fee.
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It got to a stage that if we didn't get a breakthrough, the game would have turned pretty quickly. India's No.4 was later trapped lbw by Jhye Richardson for a second-ball duck.
Casilla is positive about a possible move and sees Leeds as a great opportunity for first-team football.
Having conceded only 28 goals all season, Leeds have one of the joint-second meanest defence in the second tier.
Casilla made his first impression at senior level with Espanyol, a club he joined from Real on a free transfer in 2007 and played for over 100 times. After playing 115 LaLiga games for them, he returned in 2015 after Madrid sold similarly named but significantly more legendary keeper Iker Casillas to Porto.
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