The footballer appeared at Chester Crown Court on Wednesday for his trial.
He has already denied seven counts of rape, one count of attempted rape and one count of sexual assault.
He pleaded not guilty to the 10th charge, relating to a new complainant, which had already been reported but had not previously been put to him.
The 28-year-old, who wore a blue suit for the hearing, is alleged to have committed the offences 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 offences span July 2012 to August last year.
About 20 members of the media were in court for the hearing on Thursday, with others watching by videolink.
A French interpreter was in the dock with the defendants.
Jury selection is expected to take place later on Wednesday.
None of the women involved can be identified and reporting restrictions apply ahead of the trial.
Mendy has played for Manchester City since 2017, when he joined from Monaco for a reported £52million.
He was suspended by the club after being charged by police.
Both defendants are on bail.