R&B star Chris Brown is being investigated by the LAPD after an alleged assault on an unidentified female, TMZ.com has learned.

The LAPD is currently investigating Chris for assault following an alleged domestic violence felony battery against a woman in Los Angeles at 12:30 AM on Sunday morning.

Chris and his 20-year-old girlfriend, singer Rihanna, have cancelled their appearances at tonight’s 2009 Grammy Awards following the violent incident.

According to the LAPD, the 19-year-old star and the woman were in a vehicle on North June St. in the Hancock Park area of LA, where the victim claims an argument occurred. Chris allegedly stopped the car and the woman suffered “visible injuries;” she has identified the singer as her attacker.

“Mr Brown is a suspect that we are looking for… we would definitely like to speak with him,” a spokesperson for the LAPD said in a statement on Sunday.

Rihanna was scheduled to perform and is nominated for three Grammys at tonight’s ceremony at the Staples Center.

“We have just been informed that Rihanna will not be attending tonight’s 51st Annual GRAMMY Awards. We’re sorry she is unable to join us this evening,” a statement from the Recording Academy reads.

Chris is up for two awards at the ceremony.