According to BBC Sport, Pep Guardiola's side are said to have agreed terms with the Principality club for Mendy, 23, a France worldwide who was instrumental in his team's unexpected charge to Ligue 1 glory last season. Mendy played in 31 matches across all competitions for Monaco last season, not scoring but assisting on eight of the team's goals.
It will bring Manchester City's spending to over €200 million when you include goalkeeper Ederson, attacking midfielder Bernardo Silva and central midfielder Douglas Luiz into the mix.
The club paid £50 million for Tottenham Hotspur and England defender Kyle Walker earlier this month and manager Pep Guardiola is still on the hunt for at least one other defender, according to The Sun.
And he is to be quickly followed by the arrival of Real Madrid defender Danilo, with talks over a £26.5m move for the Brazil global progressing well.
"They are young players, with the next three, four, five years in mind", the Spaniard added.