The Brazilian spent the 2025-26 campaign on loan at Girona in Spain, and while it ended in relegation, Reis impressed and showed exactly why City spent nearly £30million to sign him from Palmeiras in 2025.
The 20-year-old now returns to Manchester, with any prospect of a second loan at Girona over given the team will be in the second tier next term.
Reis will have eyes on the first-team squad at the Etihad, a path that has become clearer with the news that Nathan Ake is set to join Turkish side Fenerbahce for around £7million.
The departure of the Dutchman would create a vacancy in the Manchester City squad for a fifth centre-back behind established quartet Ruben Dias, Marc Guehi, Abdukodir Khusanov and Josko Gvardiol.
Internally, Reis seems to be at the head of the queue.
He has already made senior appearances for the Blues, and his loan spell in Spain reinforced his ability and mentality.
Reis will likely head off on City's pre-season tour of Asia, with new boss Enzo Maresca set to be without a host of senior stars because of the World Cup.
That will open up an avenue for Reis to lay down a marker and stake his claim to be part of Maresca's thinking next season.
But the Blues must also be mindful of the homegrown rules that apply in the Premier League and Champions League next season.
Competition rules state that four players have to have come through a club's academy and four more must have come through the youth system in England for teams to be able to name a maximum of 25 players in their squads.
Regardless of whether these quotas are filled, there cannot be more than 17 players registered who are not homegrown.
Reis could potentially fall foul of the quota, as the Brazilian would not qualify, unlike Ake, Antoine Semenyo, Guehi, Marcus Bettinelli and Elliot Anderson, who all qualify as association-trained players.
As it stands, James Trafford, Rico Lewis, Nico O'Reilly and Phil Foden count as club-trained, but there are doubts over the futures of Trafford and Lewis, potentially leaving City short of association-trained players if they want to name a full quota of 25.
Unlike in the Premier League, the Champions League does not make an exception for Under-21 players who are not homegrown, so Reis, Claudio Echeverri, Sverre Nypan and others would all have to count as one of 17 if they stay with the first team this year.
In relation to Reis, City have homegrown alternatives, including Max Alleyne, who was recalled from a loan spell at Watford in January to play his part in the first team.
Alleyne would qualify as club-trained, having spent at least three years with City prior to his 21st birthday.
Eighteen-year-old Stephen Mfuni, another highly rated centre-back at the Etihad, is also an option, should he recover fully from the season-ending injury that curtailed his season on loan at Watford.
Kaden Braithwaite, who played for City's first team as a 16-year-old, is another option having captained City to FA Youth Cup glory last season.
While City won't make a first-team decision purely on the homegrown rules, it will nonetheless have to be a factor, and it's one that could work against Reis.