The victim, a man in his 40s, was punched in Alderley Heights at around 11.30pm on Saturday, March 26.
He was taken to Royal Lancaster Infirmary for treatment.
The attacker is described as in his early 20s, 6ft tall and of slim build.
He was wearing black jogging bottoms and a black puffa jacket with fur hood.
Anyone with information can call 101 or email [email protected], quoting log number 1668 of March 26.