"He will be with us barring any extraordinary occurrence," said Del Bosque.
"It would be good if he were playing (with Real) but there is only a month-and-a-half left" to the end of the season. "That will not impact upon his physical fitness," insisted Del Bosque in comments made in Madrid.
Casillas, 31, has won 143 caps and was a mainstay of the Spanish side which lifted the Euro titles in 2008 and 2012 as well as the 2010 World Cup, which booked their berth at the Confed Cup which starts in Brazil on June 15th.
But he has not played since January 23 and lost his place at Real after he broke a bone in his left hand playing against Valencia.
Since then, Real coach Jose Mourinho has preferred Diego Lopez in goal even though Casillas is back to fitness.
Del Bosque said earlier in the week in Barcelona that "we have a lot of love" for Casillas and on Friday he said he found it "a shame that some Real supporters have seen fit to criticise him".
But he said it was for a coach to decide whether to pick a player or not for their club.
Mourinho said earlier Casillas would start Saturday's league match against Betis on the bench with Lopez again preferred.