Courtois had a disappointing derby at Real Madrid on Saturday, with many fans blaming him for the 2-0 defeat.
But fellow keeper Asenjo insisted: "Ninety per cent of people who complained about his poor derby have never been under pressure in their life. Making saves is difficult, especially when you're facing one of the best strikers of ball in the world (Cristiano Ronaldo).
"Courtois did all he could. He doesn't deserve criticism, he did a good job."