The actor had his arm around friend Taryn Manning outside Boulevard 3 when her boyfriend grabbed him by the neck.
The 29-year-old was then punched to the pavement and had to be restrained by security guards to prevent him from retaliating.
An onlooker told The Sun: "The man had Jesse's neck in his hand and lifted his shirt up."
The pair were eventually separated and Metcalfe entered the club while Manning and her boyfriend headed next door.
It was reported last month that Metcalfe and Girls Aloud star Nadine Coyle have put their relationship on hold.