The 32-year-old, who captained Spain to victory at the 2010 World Cup and the 2008 and 2012 European championships, also revealed that next year's World Cup could be his international swansong, reports Xinhua.
"After Brazil, many of us will probably call it a day and make way for the younger players," said Casillas, whose Real Madrid contract expires in 2017.
"I will play as long as my head allows me to. It's more a psychological question. At the moment my objective is to see out my contract with Real Madrid."
Spain's national team trained in the rain on Thursday at the headquarters of Brazilian club Nautico, as they prepare for their Confederations Cup debut against Uruguay, to be held on Sunday.
Casillas is expected to return to Spain's starting line-up at Arena Pernambuco after five months on the sidelines for both club and country.
Despite having recovered from a hand injury in March, Casillas was overlooked by Real Madrid coach Jose Mourinho for the remainder of the season in favor of Diego Lopez.
La Roja (as the Spanish team is famously called) coach Vicente del Bosque gave a strong hint last week that Casillas would be chosen ahead of Barcelona goalkeeper Victor Valdes.
"He (Cassilas) is fit and I see him as being in the form that he's always shown," Del Bosque said.