The 28-year-old was approached at around 9pm on September 28 while in the Supercharged tent.
He was punched to the ground and while on the floor, someone stamped on his face.
He was taken to Royal Sussex County Hospital with a fractured jaw.
Detective Constable Scott Moore said: “The suspect is described as a white, short man in his late 20s with a bald head and we are appealing for anyone who saw what happened or was in the Audio tent at the time of the assault to talk to us. The victim has suffered a fractured jaw in this nasty and unprovoked attack.
“Anyone who saw what happened is asked to get in touch on 101 or email email@example.com”
Police are investigating a second assault of a man and a man has been charged for ABH for allegedly hitting a man in the face with a bottle during an altercation.
Liam Jones, 25 of Peartree Bridge, Milton Keynes has been charged with ABH and will appear at October 10 at Brighton Magistrates Court.