The 42-year-old man from Coleford had been in the Upper Bilson Inn in Valley Road where he was invited to a party by a woman he started talking to.
As he left the pub to follow the woman he was hit in the face by a man, possibly with a piece of wood.
The victim lost consciousness momentarily and suffered cuts, bruises and swelling to the face. He attended Lydney Hospital for treatment.
The assault happened in the front car park of the pub between midnight and 2am on Sunday, October 24.
Police are now eager for anyone who was at the pub that evening or in the area who witnessed the assault to come forward.
PC Debbie Davis, officer-in-charge of the investigation, said: "We need more witnesses who haven't spoken to us to come forward.
"We believe there was a large group present at the time and we need those people to think back to what they saw."
Call Gloucestershire Police on 0845 090 1234 or Crimestoppers anonymously on 0800 555 111.