Barcelona face Real Madrid in the Primera Liga at the Bernabeu on Saturday.
Valdes told Spanish newspaper El Pais: “What a keeper! It is one thing to have him in front of you and another to see him on the television.
“You already have the intuition that he is really good.
“I had never had the opportunity to work with him before and it was during the (World Cup) training sessions that you really see the capabilities of a footballer.
“Iker is impressive. The power he has. The confidence.”
