Three men followed two other men to their Brighton flat where they attacked them and stole a mobile phone.
One of the victims suffered a fractured eye socket in the robbery which happened in the street outside the flat in Percival Terrace on the seafront in Kemp Town.
The 22-year-old man also suffered a cut around his eye and a swollen face. He was taken to the Royal Sussex County Hospital for treatment.
The other victim, a 29-year-old man, was unhurt.
The three suspects, who ran off in the direction of Rock Place with the 22-year-old man’s mobile phone, were all described as black and were wearing dark clothing including dark hoods.
Detective Constable Caroline Ingold said: “This vicious attack appears to have been an opportunistic attempt at robbery.
Sussex Police said that the attack happened at about 3.20am on Friday (8 June).
Anyone who saw the robbery is asked to contact the force by ringing 101 or the independent charity Crimestoppers anonymously on 0800 555111.
