The striker has scored just one goal in seven games at international level after snubbing Brazil to play for La Roja one year ago.
Despite struggling to make an impact so far, Del Bosque is confident that Costa will start performing once he is more settled in the squad.
"I believe that a player who plays great with his club – both Atletico Madrid and Chelsea – cannot be damaging to the national team," he told FIFA.com. "I'm convinced that in the next matches he will settle in to the group. He will adapt to the group and the group will adapt to him."
Spain continue their Euro 2016 qualifying campaign on November 15 when they host Belarus.