The pair started out together at Sevilla and Casado, now plying his trade with Rayo Vallecano, claims that he always knew that his one-time team-mate was destined to do great things in the game.
"He is a reflection now of what he was then," Casado mused during an interview with Real Madrid TV.
"He has won it all at the age of 25. He is going to be a reference point [in years to come] and will beat all records.
"He will be the best centre-half this country has ever had."
Casado will share a field with his good friend once again this weekend, with Rayo set to host Madrid at the Estadio de Vallecas on Sunday afternoon.
The former Barcelona youth team player admits that taking on the La Liga leaders is a daunting challenge - but it is one to which he is looking forward.
"It will be very emotional and exciting," he enthused. "Real Madrid show the same amount of respect to the small teams as they do the big teams, and that is why the have gone 10 points clear.
"It will be a difficult game because they are the leaders and they have a spectacular group.
"They have a very good defence and then up front there is [Cristiano] Ronaldo. When [Karim] Benzema is not playing, there is [Gonzalo] Higuain; if there is no [Angel] Di Maria, there is Kaka ...
"They are stars that put on jerseys! But these are the games that you want to play in."
Rayo's clash with Madrid kicks off at 16.00CET.
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