The 32-year-old Casillas spent much of 2013 on the sidelines with club side Real Madrid after a falling out with Jose Mourinho, but was installed as first-choice goalkeeper for the tournament in Brazil, starting the opening group game with Uruguay.
Although Victor Valdes and Pepe Reina have both featured since for Spain, Del Bosque has stressed that Casillas remains his first choice for the remainder of the tournament.
"The statistics are there for everyone to see: Casillas has played over 140 games for us. I think Pepe Reina has 27 caps,” Del Bosque told AS. "All the goalkeepers are terrific, but Casillas is the one who is the No. 1.
"If you want to know who's more likely to play, it's Casillas. But they are all great goalkeepers and any of them could play."Del Bosque also revealed that midfielder Xavi considered retiring from international football following the Euro 2012 final win over Italy, but stressed that the Barcelona star was never likely to call time on his Spain career.
"Xavi felt a little uneasy at that time and we had a conversation, but it never got serious. Xavi is our leader on the pitch, the one who manages the team from inside and who dictates the play. Of course I am going to talk with him," Del Boqsue said.
Spain could face host Brazil in the final should the Selecao successfully navigate their semifinal against Uruguay, and Del Bosque suggested he would be worried by the defensive capabilities of Luiz Felipe Scolari's outfit.
“Brazil have terrific players like Marcelo, David Luiz, Thiago Silva and Dani Alves. Alves is a great player who has brought a lot to the Barca team,” Del Bosque said.