Del Bosque wants the 25-year-old to prove himself, although he admits he does feel a certain obligation to the former Braga forward.
"Diego Costa does not have unlimited credit," Del Bosque said in a press conference.
"It is true that we feel a bit of an obligation, but the final decision will be based on his performances over the course of the season.
"It was a hard and risky decision for him as he changed his dream of playing for Brazil to defending Spain's honour instead.
"He brings healthy competition to the team in attack and we will select those who are the best.
"There are still enough matches to prepare for the World Cup and he will get his chance."
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