The Barca goalkeeper was wary of his fellow stopper's ability, despite his exile from the Real Madrid team last season, while he reiterated his desire to leave Camp Nou next term
The Real Madrid goalkeeper fell out of favour last season following a reported bust-up with then-coach Jose Mourinho, thus prompting fears that the 32-year-old could no longer be regarded as indispensable by La Roja.
However, the Barcelona man insists Casillas is in "top form" despite his lack of match sharpness and is ready to prove his worth to Spain boss Vicente del Bosque during the Confederations Cup.
"[Casillas is] doing well, he's the same as always; on top form and raring to go. He's very motivated, on and off the pitch. It's important we have a healthy competition, because that will benefit the team.
"I cannot reveal [who is No.1]. I am just another member of the squad and that has been the key of this team's success.
"I will do what I am asked, and Del Bosque will decide. I am just grateful to be here, I have felt like the happiest child in the world since I was called up to the squad for the World Cup.
"It is a privilege to play with Spain and to be part of this team."
Valdes announced at the tail end of the 2012-13 campaign that he would not renew his contract with Barca beyond next season, but while he admits his stance has not changed, he will see out the remaining year of his deal in Catalunya.
"My situation at Barcelona has not changed. I have one year left on my contract, which I'm going to complete, and I'm not going to renew," he added.
"I am grateful for the club’s offer but nothing has changed. I have always been honest with the club."
The Blaugrana recently concluded a deal to bring Neymar to the Camp Nou outfit and Valdes - despite his intention to move on in the coming year - is chomping at the bit to play alongside the Brazilian forward next term.
He said: "He is one of the best footballers around at the moment and I celebrate the fact he has joined us because the best players in the world need to play for Barca. He will help us to keep winning."