It is reported that Chris Brown was spotted flirting with singer Leona Lewis just hours before he was accused of assaulting his girlfriend Rihanna.

The Daily Mirror reports that the R&B star was spotted chatting to the British singer and 'X Factor' winner Lewis at a pre-Grammy awards party in Los Angeles on Saturday night.

The newspaper reports a source as saying: "Rihanna saw Chris flirting. He and Leona were laughing and Rihanna saw his hand on the small of her back."

The couple later left the party after which the incident is alleged to have taken place.

TMZ.com quotes police sources as saying 20-year-old Rihanna lost consciousness during the alleged attack in the early hours of Sunday morning.

Brown later presented himself at a police station for questioning and was then released on $50,000 bail.

Rihanna was treated at Cedars-Sinai Medical Center for swelling and bruises in the early hours of Sunday morning.