A store manager was beaten unconscious on the pavement after refusing to sell beer to teenagers.
His nose was broken and his face badly cut and bruised in the attack, which happened outside the Londis store in Kingsway, Hove.
Minutes earlier the manager had turned three teenagers away from the shop after they tried to buy alcohol.
The group left the shop but one of them returned a few minutes later and bought a packet of cigarettes before rejoining the others outside.
The manager noticed they were hanging around outside the shop and went out to ask them what they wanted.
Sergeant Richard Delacour, of Hove police, said: "The next thing he remembers is waking up as he was being put into an ambulance, which was called by a passer-by.
"We believe he was attacked by one or more of the group he went outside to speak to.
"He cannot remember anything about the assault but was able to give us a clear description of the youths who were in the shop and who he spoke to outside."
Although the Londis store does not have its own security cameras, the nearby Unwins off-licence does.
Police were told three youths matching the descriptions given by the victim had been in Unwins shortly before the attack took place.
They had also asked to buy alcohol but were refused by the manager.
Police have released these CCTV images of the group waiting to be served at Unwins.
Mr Delacour said: "This was a completely unprovoked and violent assault and it is fortunate the victim's injuries were not far more serious.
"We would like these three individuals filmed in Unwins to come forward so we can eliminate them from our inquiries if they were not involved.
"We would also like to hear from anyone who knows them or who witnessed the assault on July 10 at about 9.40pm."
Anyone with information should phone PC Gail Selleck at Hove police station on 0845 6070999.
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