Vincente del Bosque's men crashed to a second consecutive defeat, losing 2-0 to Chile in Wednesday's Group B clash in Rio de Janeiro - ending their hopes of retaining the World Cup trophy.
It was the first time Spain had suffered back-to-back defeats since losing two consecutive games against Northern Ireland and Sweden during Euro 2008 qualifying.
Many believe it is the end of a cycle, with goalkeeper Casillas (33), Xavi (34), Xabi Alonso (32), Andres Iniesta (30) and Fernando Torres (30) now in their 30s.
But Casillas stressed it was not the time to discuss the futures of some of the country's older players, with one game against Australia still to come in Brazil.
"If in a World Cup you lose the first two matches it explains everything," Casillas told reporters post-game after Spain followed on from Italy, who failed to advance from the group stage as defending champions in 2010.
"We ask for people's forgiveness, though hopefully they know that we did everything possible to make them happy again. But it wasn't to be.
"We are the first people responsible and we are very hurt. It's been a tough blow and we need to take it.
"I don't think we need to talk about that. This is not the day to start blaming people and discussing whether to change or not change.
"There are some players who are over 30, the coach will make his decisions and we will respect them."
Casillas came in for criticism following Spain's 5-1 capitulation to the Netherlands in the opening game and while he refused to be drawn into his own future, the Real Madrid shot-stopper said the team wanted to leave South America on a winning note.
"Was that my last match? I don't know, we'll wait and see. This group doesn't deserve an ending like this," he added.
"Now we need to try and finish in the best possible way against Australia. All we can do is congratulate Chile and look to the future. Chile played very well.
"When you are out of luck and you aren't in form at the World Cup, this is what happens. No one expected anything like this.
"This is football. Four years ago we went through the positive side of it and now we get the negative side."
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