Chelsee Healey was punched in the head during a night out with friends.
The 24-year-old former Waterloo Road star, who was partying in central London with BFF Tulisa Contostavlos, was reportedly attacked while outside the DSTRKT club.
A furious Healey had to be held back by friends after the attack but was later seen breaking down in tears.
"Chelsee was having a drink and dance and at about 2.30am she stepped outside the club," a witness told the Sun.
"All of a sudden this girl ran up, punched her in the face and then legged it. It was a horrible end to a good night."
Healey who reported the incident to police after the attacker ran off - vented her anger online following the attack.
"So a girl thinks it's nice to punch me in the side of my head on the sly n run off lol. I seen u, you fat mess, wish I wuda caught u tub," she told her 164,000 Twitter followers before deleting the message.