The Spanish goalkeeper has reclaimed his spot as number one at the Santiago Bernabeu following the departure of Diego Lopez to Milan but was the subject of whistles in Saturday's 2-1 defeat to rivals Atletico Madrid.
It marked a second successive defeat for Carlo Ancelotti's side with Casillas bearing the brunt of frustrations from certain fans.
However, the 33-year-old impressed in Real's 5-1 demolition of Basel in the UEFA Champions League and was warmly applauded after a smart save from Derlis Gonzalez in the second half.
While Ramos believes his Spain and Real team-mate can cope with criticism, the defender also suggested the whistles had affected him.
"I will not get into a debate, it would be stupid. Above all is the club and we focus on that," he told AS.
"Iker can live with it, he knows that he can't please everybody.
"He is not a robot and the whistles affect him."