US musician Usher. Picture: Supplied/Bang Showbiz

Usher has asked for a $20 million  (R263 million) lawsuit accusing him of giving a woman herpes to be thrown out.

The 'OMG' singer is being sued by an unnamed woman in Georgia, who claims she contracted the sexually-transmitted disease from him in April, and he has now filed a response to her case.

In legal documents obtained by TMZ, Usher noted the lawsuit didn't state whether she had been tested for the disease before their alleged sexual encounter.

He said: "A previous sexual partner very well may have already infected her."

And he also argued she could have contracted the infection from someone else after they allegedly slept together, and claimed she assumed the risk of getting herpes by having "casual, unprotected sexual intercourse and/or oral sex."

Usher's lawyer also objected to the alleged victim, who is known only as Jane Doe, using a pseudonym, claiming there was no cause for her to file the lawsuit in secret.

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The woman initially sued for $10 million (R131 million), but after a test showed she'd contracted the virus, she upped her bid to seek at least $20 million for emotional harm, medical bills and punitive damages.

The woman isn't the only person to be suing the 38-year-old singer - who paid a woman $1.1 million (R14.5 million) in 2012 to settle a lawsuit after she claimed to have contracted herpes from him - for allegedly putting them at risk of having the sexually-transmitted disease.

Only one of his accusers has been publicly named, 21-year-old Quantasia Sharpton, and she recently claimed she took action against the 'Confessions' singer for not disclosing that he allegedly had the infection because she felt her "rights were violated".

She said: "I had a child a year ago, and I knew I was negative. But I contacted [lawyer] Lisa Bloom to find out what my rights are as a woman. 

"Although I am negative, I am upset by the reports because I never would have consented, if I would have known. I would not have taken a risk of getting an incurable disease.

"My health is very important to me, now that I am a mother. I feel that my rights were violated. 

"I am speaking out today on behalf of myself and others, some of whom are positive and are embarrassed to speak out publicly. I am doing this so that he does not do this to anyone else."

And the woman urged Usher to speak out and confirm whether or not he has the condition.

She added: "Usher, if you are negative, please say so. If you are positive, you need to warn your sex partners, so that they can make their own informed decisions."