The deal, reported by French journalist Fabrice Hawkins and subsequently confirmed by RMC Sport and Foot Mercato, represents Manchester City's move to lock down one of the brightest young talents within their own City Football Group network before outside interest could develop further.
Troyes, a City Group club, won the Ligue 2 title this season to secure promotion to the top flight. Detourbet was central to that campaign, contributing four goals and seven assists across 27 appearances. His contract with Troyes runs until 2028.
VfL Wolfsburg were among the clubs pursuing him seriously, holding several rounds of talks earlier in the year. A number of other Bundesliga clubs and AS Roma also registered interest. None succeeded.
City have now concluded a deal with Troyes, and an agreement with Monaco for a season-long loan — with the option of a further year — is already in place between all three clubs. Only the player's personal terms with City remain to be formalised, though those are expected to be resolved quickly.
The loan structure reflects the nature of the opportunity for Detourbet. Monaco, who are targeting Ligue 1 competition next season, offer regular top-division minutes at a level considerably beyond where he has been operating. City, meanwhile, are unable to immediately integrate a player of his age and profile into their first-team environment.
The move also fills a gap on Monaco's side. The Principality club are bracing for the expected departure of Maghnes Akliouche, and Detourbet's profile as a right-footed wide forward fits the space that exit would leave.
The transfer cements a pattern City have used before — develop a talent within the network, acquire before the market inflates the price, then place the player in a stronger loan environment until he is ready for England.