Casillas will battle new signing Keylor Navas for the gloves at the Bernabeu in the new campaign.
"It's not an easy decision but if I was the coach, I'd pick Iker. He is very good, very happy. The World Cup wasn't good for him or for Spain but that's the past," he told AS.
"If you see the European Super cup against Sevilla you realise he is where he should be and he made several stops that prevented the game getting complicated.
"It's hard to be 100% sure but I'm convinced Madrid has a great Casillas back, because he has the mentality and feels the colours in his heart. I think it's very good to have two goalkeepers who can play. Keylor had a great World Cup and won a lot of confidence. That's good for Madrid."
Casillas was Madrid's first-choice goalkeeper in the Champions League and Copa del Rey last season, but played second fiddle to Diego Lopez in the league.
Lopez has since moved on to AC Milan, but Navas will provide the competition this time around.