The Desperate Housewives star was leaving London nightclub Studio Valbonne on Saturday night when he reportedly attacked paparazzo Rowan Lawrence, leaving him with a bloody nose.
Lawrence said: "He was coming out of the club and walking towards his taxi. But he kept walking past the vehicle. I was walking backwards away from him and he kept walking towards me. He then raised his fist and punched me in the face."
He reported the incident to Charing Cross police station and has asked for criminal charges to be brought against Metcalfe.
The actor spent the rest of the night watching girlfriend Nadine Coyle's band Girls Aloud play at a World AIDS Day event at G-A-Y.