The singer insists he was not with a second accuser on the night she claims she contracted a sexually transmitted disease from him.
Usher is fighting to have a $20 million (£15.3 million) lawsuit, filed by a woman who claims the singer gave her herpes, dismissed.
The Georgia woman accused the Yeah! hitmaker of infecting her with the sexually transmitted disease last month (Jul17).
The star denies her accusation and claims her lawsuit does not mention whether she was tested for the illness before she began a sexual relationship with him.
According to documents obtained by TMZ, the 38-year-old alleges, "A previous sexual partner very well may have already infected her."
Usher also maintains that she could have contracted herpes from someone other than him after their encounter and put herself at risk by having "casual, unprotected sexual intercourse and/or oral sex."
He is asking a judge to toss the suit.
Meanwhile, Usher previously told friends he was never with Quantasia Sharpton, another woman who is suing the singer for putting her at risk of contracting a sexually transmitted disease.
The star, who is facing a lawsuit from the 21-year-old, has denied claims he had sex with her at a Days Inn hotel in Atlantic City, New Jersey.
Sharpton claimed one of Usher's aides took her phone number after he spotted her in the crowd at a concert, and they later arranged to meet at her hotel. But she alleges Usher never mentioned he had herpes, which she contracted.
Sources close to Usher claimed that he was too busy falling in love with Grace Miguel, his manager and now wife, at the time of the incident.
The insider adds that on the night of the Atlantic City show, the set ran late and the singer had to push back his post-show meet-and-greets until after midnight, proving he could not have been with Sharpton, who claimed that they were at the hotel around 12am.