The Atletico Madrid forward has come to a decision on which country he wishes to represent at the international level, but declined to reveal his choice.
The Atletico Madrid striker has been in impressive form this season, firing the Rojiblancos to second in La Liga with 10 goals domestically in 2013-14 and adding two more to his tally in Tuesday's 3-0 Champions League win over Austria Vienna.
Costa has already featured for Brazil in friendly fixtures but is eligible to swap to Spanish nationality, something he has expressed an interest in.
"My decision has been made," he told reporters in Vienna. "But this is not the right time to make it public. People who need to know already know. I have no doubts about what I will do. But I must wait for the right moment. If I could say which, I would have done so long ago."
Vicente del Bosque has expressed his desire to bring Costa to la Roja's setup ahead of next summer's World Cup in Brazil, though Luiz Felipe Scolari has been vocal in his desire to keep the 25-year-old attacker as a Brazil international.