Club captain Casillas has solely been used in the cup competitions by Carlo Ancelotti this season with Diego Lopez starting every Real fixture in La Liga.
However, Valdano, who left the Bernabeu in May 2011, believes the 32-year-old should start their remaining league fixtures to ensure he is ready for the European final against city rivals Atletico Madrid.
If Ancelotti persists with his current selection process, Casillas will not feature again until the showpiece in Lisbon on May 24 - some 25 days after Real's semi-final victory over Bayern Munich.
And Valdano has called on the former Milan, Chelsea and Paris Saint-Germain boss to ditch his preference for Lopez in Real's final four Liga games.
"Casillas not playing until the final is a problem," he told Cadena Ser.
"I would give him minutes. It's a long time without playing."
