The Atletico trainer discussed his striker switching to Spain, and claims he is unperturbed at being omitted from the World Coach of the Year award
On Tuesday, the Brazil-born marksman ended weeks of speculation by officially announcing he would be switching allegiances from the country of his birth to la Roja, much to the frustration of the Brazilian Football Federation (CBF), whose chiefs have called for the 25-year-old to be stripped of his citizenship.
However, Simeone has lept to the defence of the Atleti hitman, stating that Costa - who is eligible for Spain via five-year residency - has his respective reasons for making the switch.
"I never influenced him personally and collectively - he was always influence by what the team needed," the coach told a press conference.
"Surely this will give him more peace of mind to focus on what he has to do for the future with the Spanish national team and with us, to keep doing the same.
"Decisions are decisions. When one makes a decision, he has already evaluated the reason to take it. Those who think and look from outside are not taking this decision.
"Diego has shown what he wants and now he has to keep giving everything every day."
The former Argentina international guided the Rojiblancos to Copa del Rey glory last season at the expense of bitter rivals Real Madrid, but failed to earn a nomination for Fifa's World Coach of the Year award.
However, the 43-year-old claims that he is unperturbed by the exclusion, insisting that he does not concern himself with individual honours.
He added: "I have always said that I do not look for credit in different places, I just try to do good in the eyes of the people who employ me.
"I have to continue working with my team, with my players, and trying to do my best for the club and that is what matters most to me."
Costa, who has hit 11 goals in 10 appearances for the capital club in La Liga thus far this season, earned two caps for the Selecao at senior level, both coming in friendlies earlier this year.