The 30-year-old joined City from Portuguese outfit Porto in 2014 for a fee of £12m.
The midfielder made 101 appearances in all competitions for City, scoring four goals in the process.
The player made just five Premier League starts last season and the writing was on the wall when he was left out of Pep Guardiola's pre-season tour squad.
Fernando is expected to finalise his move to Turkey in the coming days.
Fernando on Instagram: "Together for the new challenge!"
— City Watch (@City_Watch) July 30, 2017
Transfer to Galatasaray imminent? pic.twitter.com/iZ1279766S