Fernandinho has already returned to boyhood club Athletico Paranaense in his native Brazil.
Fernandinho joined Manchester City from Shakhtar Donetsk in the summer of 2013, spending nine seasons with the Citizens.
The former Brazil international was a faithful servant at the Etihad Stadium, winning five Premier League titles, six League cups and one FA Cup.
He also made 383 appearances in total for Pep Guardiola's side and scored 25 goals.
"I saw. I saw my family proud. I saw supporters that never forgot where they came from," Fernandinho posted in an open letter on Twitter.
"I saw the beauty of being part of a winning team. I saw titles, superstars and geniuses. I saw an opportunity to fulfil my dream.
"And then I realised. I realised the importance of all reading this letter. I realised that I made the right choice, the best choice of my entire life.
"I hope one day when you remember me, you feel the same way that I'm feeling when I'm writing this."
He added: "Athletes, coaches/trainers, laundry staff, kit managers, cleaners, concierge, security team, door staff, advisors, executives, cooks, directors, doctors, masseuses, physiotherapists, sports psychologists, media team, analysts, youth teams, charity teams…
"Apologies if I missed anyone, but you know who you are. Today is the last day of my contract with Manchester City.
"I can only say that I gave my very best and I would do it all over again. The story continues and after playing for nine years, I will become an avid Cityzen supporter for many more titles and victories.
"I am certain that many more will come judging by the quality of all your daily work."
"My memories will last forever. Many thanks, your eternal captain."
