The former France international's lawyer had said Nasri was sanctioned for receiving an intravenous drip treatment at a clinic in Los Angeles in 2016, when he was on loan at Sevilla from City.
"The player Samir Nasri is suspended for eighteen (18) months. This suspension will start running on 1 July 2017," UEFA said in a statement on their website.
"The player Samir Nasri is allowed to return to training, with any football club starting from 1 November 2018."
UEFA said Nasri's amended suspension was a result of negotiations between the player, WADA, the French Anti-Doping Agency and UEFA's Ethics and Disciplinary inspector, who originally believed a two-year suspension was warranted.
(Reporting by Aditi Prakash in Bengaluru; Editing by Peter Rutherford)
