The 24-year-old scored eight goals and provided 11 assists in 47 appearances across all competitions for Manchester City, operating under a contract that runs until the summer of 2028.
Transfer journalist Nicolo Schira reported in early June that Doku was closing in on a contract extension with City.
Fabrizio Romano now reports that City and Doku have agreed terms on a new deal, with the two parties said to have reached a verbal agreement and final details expected to be finalised shortly.
The new contract would run for five years, until the summer of 2031, and is reported to include a pay rise for the Belgian.
Romano added that Doku is expected to sign the contract soon, and that team-mate Josko Gvardiol is also set to put pen to paper on a new deal of his own in the near future.
Manchester City finished second in the Premier League last season, and manager Pep Guardiola has since left the club, with all indications pointing toward Enzo Maresca taking over in the dugout.
The timing of Doku's renewal, alongside Gvardiol's, suggests City's hierarchy are moving to lock down key performers from last season's squad regardless of the managerial change, providing some continuity for whoever takes charge of integrating a rebuilt midfield and a new attacking structure around the existing core.
Doku has established himself as one of the Premier League's most dangerous one-on-one attackers since his move from Rennes, with his pace and dribbling ability making him a regular threat from the left flank under Guardiola's possession-based system. City paid around £55m to sign him three years ago, and his new terms reflect a significant rise in his standing within the squad since then.
A new long-term contract for Doku, combined with City's pursuit of Elliot Anderson in midfield, points to a club moving with intent through the early weeks of the post-Guardiola era rather than waiting for a new head coach to be confirmed before making major decisions on the playing squad.