According to statement released by Sussex Police, there was an altercation involving several men in Surrey Street, Littlehampton, at about 6.30pm on Sunday, January 20.
One of those involved, a 54-year-old local man, fell into the road and sustained a fractured jaw and other facial fractures, for which he is still receiving out-patient treatment, police said.
Detective Constable Lee Simmonds said: "The reasons for this incident are not yet clear but these are serious injuries and we need to discover who caused them."
If you can help, contact police online or call 101, quoting serial 0897 of 20/01.
You can also contact the independent charity Crimestoppers anonymously on 0800 555 111.
No arrests have yet been made, police said.