Despite playing only 22 senior games for Palmeiras, City moved swiftly by spending £29.6m to sign Reis in January 2025.
It was the same month in which they brought in Abdukodir Khusanov and while the Uzbekistan international has established himself as a first-team regular, Reis has managed only four games and was sent out on loan to gain more experience.
His time at Girona did not start particularly well, sent off in only his fifth game against Levante in September and he had to adapt to a new country, new team-mates and find consistency in his performances.
But Riera says he improved game by game and things clicked by the end of November and by the end of the season, he was one of the players who manager Michel “could rely on”.
“He improved a lot in physical terms,” Riera added. “In the beginning he was not that consistent in the duels and that is what people told me before he arrived – he was skillful but not that strong.
“He became stronger in the duels and Girona played very offensive football so there were wide spaces in behind him, but he was always able to run quickly backwards towards his own goal as well as forwards.
“Once he became a physical player, he was almost unbeatable. He was one of the best defenders we have had at Girona in the past few seasons.”
Despite boasting a squad containing household names Donny van de Beek, Daley Blind, Axel Witsel, Thomas Lemar and Marc-Andre ter Stegen, Girona won only nine of their 38 league games and were relegated by a solitary point.
Reis will be given the opportunity to make an impression on City’s trip to the Far East next month as he aims to nail down a first-team spot, but may still end up going out on loan again should the current plan not work out.
“If Girona stayed up in La Liga, many fans will have hoped he could have spend a second season on-loan at the club,” Riera added. “After relegation, that is not possible.”