He had already denied seven counts of rape, one count of attempted rape, and one count of sexual assault.
The defender pleaded not guilty to the 10th overall charge, relating to a new complainant, which had already been reported but had not yet been put to him.
Mendy, 28, entered the plea as he appeared at Chester Crown Court on Wednesday for his trial.
The defender, who wore a blue suit for the hearing, is alleged to have committed the offenses against seven young women between October 2018 and August last year.
He is due to stand trial alongside co-defendant Louis Saha Matturie, 40.
Matturie, of Eccles, Salford, denies eight counts of rape and four counts of sexual assault relating to eight young women.
His alleged offenses span July 2012 to August last year.
Jury selection is expected to take place later on Wednesday.
Mendy has played for Manchester City since 2017 when he joined Monaco for a reported £52m.
He was suspended by the club after being charged by police.
Both defendants are on bail.