Nine goals in seven games has shown why Chelsea splashed out on him over the summer, and La Roja are hoping to take advantage of that form.
Midfield playmaker Koke is one who is delighted to see him shake off any fitness concerns.
Koke played alongside Costa at Atletico Madrid last season, and knows the striker will make his own job easier.
He told AS: "He is a player with a great eye for goal and that fits well with the team. In England he is showing everything, he has been good so far.
"Diego has to come and play for us, and we have to look for him when we have spaces and breaks, because his movement can put us in position to score."
After much hype over his decision to play for Spain, rather than Brazil, Costa's World Cup was a disappointment - playing only twice and failing to score as the defending champions crashed out in the group stages.
He is yet to score for his adoptive country, and will be hoping to put that right in their upcoming Euro 2016 qualifiers.
The 26-year-old has been in stunning form since signing with Chelsea however, and the hope is around the Spain side, that his national side will finally see the best of him.