El-Haddadi, who scored on his league debut for Barca this season, was already with the Under-21 side and Del Bosque has claimed that the 19-year-old was the natural choice as Costa's replacement.
"It was a logical and natural solution [to call-up Munir]," Del Bosque told Spanish television, according to AS.
"For one thing [Albert] Celades had already called him into the Under-21s. We named Munir because he was already at the training complex."
El-Haddadi only made the breakthrough into the Barcelona first team this season.