The former Atletico Madrid defender posted to social media: "Hello to you all.... Today I'm here to make a statement about my future.
"I've been thinking a lot over the last few months and, together with my family, have made a decision about my future in football. There were great moments lived, a career I can only be thankful for, playing in great clubs, four different countries, the Brazilian national team and a lot of history to tell for the rest of life.
"But it's time to leave the lawns and the idea is to put an end to the season here in Nottingham Forest, England. It's still early to explain the reasons, something I will do in the future, as I still have a contract and I want to honour him as I always did for all the clubs I defended.
"But out of respect to the clubs that have been looking for me for the future and even to my current club, I wanted to come here to advance this issue and speak with an open heart and honesty. Thank you and let's make the most of these last months in the best way possible, with lots of joy, intensity and dedication."