Casillas, the Real and Spain captain and a fixture in both teams for more than a decade, sustained the injury during a King's Cup game in January when team-mate Alvaro Arbeloa kicked his hand while trying to clear the ball.
Real coach Jose Mourinho brought in Diego Lopez from Sevilla as cover and although the break has healed the Portuguese has left Casillas out of the team, fuelling speculation about a rift between the pair.
"We know that he is a legend of Spanish football, that nobody has achieved what he has, and then in 10 days he is put in an uncomfortable situation," Del Bosque said.
"I don't imagine that in England they would question [Peter] Shilton in this same situation or other players that have been legends in their national teams," added the former Real coach.
"We therefore are obliged to protect players that have given so much to the national side."
Lopez, a former Spain international who came through Real's youth ranks and had a five-year stint at Villarreal, has been in fine form since returning to his boyhood club.
"The important thing is that he [Casillas] is recovering, he is training and we have time to take any decisions," Del Bosque said.
"I must say that he is our player, one of the best that has represented us in more than 140 games and we have a lot of affection for him. It is normal that he would be with us [at the Confederations Cup]."
