Casillas has been under pressure at both club and international level over the last 12 months or so following a series of high-profile mistakes and his form is now being seriously scrutinised.
However, Pique has backed his international teammate, and insisted that the collective must be blamed for Thursday's shock 2-1 defeat to Slovakia in Euro 2016 qualifying.
"He is a professional without a doubt – the best in the world in his position," Pique told reporters at a press conference.
"Having him as a teammate and as our captain is marvellous as far as I'm concerned. I don't think anything went right for anyone in particular against Slovakia."
Real Madrid stopper Casillas is expected to continue in goal for tonight's Euro 2016 qualifier against Luxembourg.