The two clubs are still in talks over the transfer and have not yet finalised the details. Given the Turkish club's confidence, the move is expected to go through this summer, ending Ake's six years at the Etihad.
A fee of around £7m, potentially rising to £8.5m, has been discussed between the two clubs. There will have been bemusement in Manchester, though, that Fenerbahce chose to announce a deal that is not yet complete.
Fenerbahce's statement read: "Our club has reached an agreement with Nathan Aké, a player of the Netherlands National Team, and has signed a contract with the footballer."
The statement continued: "The player, who wore the Netherlands jersey in the 2026 FIFA World Cup, will join our team in the Austria camp following the permission process."
Ake's departure will leave Manchester City with four senior centre-backs following the earlier free transfer exit of John Stones.
Ruben Dias, Josko Gvardiol, Abdukodir Khusanov and Marc Guehi remain a formidable quartet, but Enzo Maresca will need to bolster those numbers to compete across multiple competitions.
Brazilian defender Vitor Reis, who spent last season on loan at Girona, could return to provide extra cover.
Homegrown centre-back Max Alleyne is another option, having answered an emergency call from City in January and terminated his loan at Watford to make his first-team debut.
Manchester City are also relying on academy goalkeeper Oliver Whatmuff for pre-season, despite the teenager joining Stockport County on a season-long loan announced on Wednesday.
Whatmuff is likely to be in Seoul rather than Stockport at the start of August, needed to bolster Maresca's goalkeeping options. Gianluigi Donnarumma is available after Italy failed to qualify for the World Cup, and third-choice goalkeeper Marcus Bettinelli is also free to travel.
There is separate interest in academy graduate Pierce Charles, who has spent the last five years at Sheffield Wednesday.
With second-choice keeper James Trafford currently with England in the United States, and City returning for training in just over a fortnight, Whatmuff has been picked as cover for the first-team squad.
He will report to City in the week of 20 July, having started for Stockport, and is likely to travel to Asia for City's two-week pre-season tour.