An assault victim required emergency surgery after being punched in the head.
The 45-year old man was walking along Norfolk Road, Littlehampton, between 10.45pm and 11.15pm on Wednesday when he was approached and punched by another man.
The offender then got into a silver Mercedes, which is believed to have had other occupants, and it drove off from the scene.
The suspect is described as white, of stocky build, with bald or close cropped hair, and wearing light coloured shirt and trousers, possibly Chinos. It is believed that he is of Eastern European origin.
It was later established that the victim had suffered a serious head injury as a result of the assault, requiring immediate surgery at the Hurstwood Park Hospital in Haywards Heath.
He has since come out of surgery and is currently described as being in a stable condition.
Detective Sergeant Colin O'Hare said; "The motive for this incident is not yet known, and at present it appears to have been a random attack. However enquiries are at an early stage and we are appealing for any witnesses to contact us at Worthing CID via 101 or email email@example.com quoting serial 1796 of 18/6. You can also call the independent charity Crimestoppers anonymously on 0800 555 111."