Brazilian side Paranaense confirmed on Tuesday (AEST) that an agreement is in place to re-sign Fernandinho, who previously spent three years with the club.
The 53-cap former Brazil international left Paranaense in 2005 to join Shakhtar Donetsk, before spending nine seasons with City, the last two of those as captain.
After making 383 appearances for City and winning 12 major honours, including five Premier League titles, Fernandinho bowed out at the end of the 2021-2022 campaign.
And on the day his contract at the Etihad Stadium officially expired, Fernandinho took to Twitter to pay an emotional tribute to everyone connected with City.
"I saw. I saw my family proud. I saw supporters that never forgot where they came from," he posted in an open letter.
"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 said: "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."
Fernandinho signed off the letter: "My memories will last forever. Many thanks, your eternal captain."
The 37-year-old previously revealed he turned down numerous offers to return to Paranaense, who are now managed by former Portugal and Brazil boss Luis Felipe Scolari.