A run of disappointing form for Spain saw the Real Madrid goalkeeper replaced by David de Gea in Saturday's victory over Luxembourg, but he insists that he can still be an important member of Vicente del Bosque's squad.
"I'm not immortal," Casillas told reporters. "I won't last forever but, at the moment, I feel good and believe I can help my country qualify for the Euros.
"After you fail to win a game, all sorts of things go through your mind; you feel angry. It's like when you have an argument with your brother and you think 'I'll kill him', but you don't mean it. I want to keep playing for the national team for as long as possible while the gaffer wants me."
Casillas has won 158 caps for Spain since making his debut in 2000.