The 24-year-old has spent his entire senior career in Europe, firstly in Portugal before being snapped up by Atletico in 2007.
Costa, who was the subject of a summer bid from Liverpool, has begun the season in superb form and is currently top scorer in La Liga with ten goals - equalling his previous highest ever total in a full campaign.
Now Costa is preparing to finalise the paperwork to confirm his Spanish citizenship, after which point he is expected to receive a call-up.
Costa says that they are just now awaiting confirmation from FIFA about his switch of allegiance.
"I don't get involved. What's most important for me is to keep on working," he told AS.
"It's up to FIFA to make the decision. The decision to play for Spain has already been made.
"Spain has given me everything and if I can play for the national team I will do it as well as I can."
Brazil's FA vice-president Marco Polo del Nero told Estado de Sao Paulo over the weekend that they would not make any protest.
"The Brazilian FA believes in free will, if a player wants to play here or there, it will not be this organisation that will say he can't," he said.