Simao joined Atletico in 2007 for 20 million euros from Benfica and believes he has given his all in the Spanish capital.
He said: "I don't think I have defrauded anyone. It is difficult for me, I can hardly speak because since I came to Atletico I have grown and become a better professional.
"When I arrived I said I would do my best to win a title and I eventually ended up with two in Europe (the Europa League and the European Super Cup).
"I have to thank the fans, the support they have given me has been spectacular. I will continue to follow Atletico as a fan myself."
Atletico president Don Enrique Cerezo hailed Simao's contribution over the past three-and-a-half years.
"We are here today to say farewell to a great player who has had so much success with Atletico Madrid," he said.
"And we are here, above all else, to say farewell to a great person who we have all been privileged to know over the past few years."