The France international left-back has impressed this season and has been instrumental in guiding the Ligue 1 club back to the top of the league, and into the quarter-finals of the Champions League. He has provided 10 assists in 33 games from his defensive position – the highest for a defender in all five top European leagues.
According to Sky Sports, Jose Mourinho, Antonio Conte and Pep Guardiola are keen on signing a left-back in the summer and have identified Mendy as the perfect candidate. The defender joined Monaco in the summer of 2016 from Marseille for a fee of around £13m ($16.2m), but it is believed that he is now worth double that amount closer to the £30m mark.
United do not have a regular left-back, with a number of players occupying the position this season. Luke Shaw, the left-back United signed from Southampton for over £20m, has failed to meet expectations after returning from a long-term injury. Despite criticising him, Mourinho has chosen to give him another chance to impress before the end of the season.
Chelsea have joined the race for Mendy with Antonio Conte looking to bolster his ranks ahead of the Blues' return to the Champions League next season. Marcos Alonso is the Italian manager's only option in the left wing-back position at the moment, and is keen on bringing the 22-year-old Frenchman, who is as adept in attack as defence, to Stamford Bridge.
City are also actively looking for a left-back as a replacement for Gael Clichy, who is out of contract at the end of the season. The club are yet to offer the former Arsenal defender an extension and could allow him to leave on a free transfer.
Guardiola has always preferred attack minded full backs at every club he has managed and Mendy, who has shown that he has the penchant for involving himself in attack, will be perfectly suited to the Spanish manager's style of play at the Etihad Stadium.
However, Mendy is contracted to the Principality club until the summer of 2021 and they will be reluctant to sell a key player after just one season. Especially since they will be competing in the Champions League again next season and most likely will also be defending the Ligue 1 crown for which they are the current favourites ahead of Paris Saint-Germain and Nice, who are in second and third place respectively.