Costa fit for El Salvador clash
The Atletico Madrid forward's fitness has been all the rage after he suffered a hamstring injury in early May - an ailment that limited him to just nine minutes in the UEFA Champions League final.
However, Del Bosque said Costa was fit again, and would state his case for selection in the US friendly ahead of their Group B campaign against Australia, Chile and the Netherlands.
"Diego will play tomorrow," Del Bosque said on Friday.
"He had a good training session today, he felt good.
"We want him to play and check how he feels, especially after a while since the last that he played a complete match."
Despite Atletico coach Diego Simeone deploying the power forward too early in his recovery in the European final against Real Madrid, Del Bosque had no concerns Costa was being rushed back into the team prior to the World Cup.
"If we thought that there was a risk for Diego Costa playing tomorrow, we wouldn't use him tomorrow," the 63-year-old said.
"We think that he's fine, his medical situation is done, he's ready so we want him to play."
Del Bosque indicated he would be making wholesale changes to his starting XI, after their 2-0 win over Bolivia in late May.
"We are in our second week of training and we're going to use specially those players who weren't able to be here in the first week," he said.
The situation of striker David Villa, who has signed for MLS outfit New York City FC and also secured a guest stint at A-League side Melbourne City, was of no concern to Del Bosque.
"We are specifically focused on the World Cup, not in their future," Del Bosque.
"They have their own agents who look after their interests and it's been a fact that several players that were in our league are leaving to other leagues.
"David's situation is not unique."