A spokesman for Sussex Police said a man in his 60s was hit by a car in a layby along the A283 just before 6.30pm on Wednesday, June 5.
The car then drove off, the spokesman added, and the victim was treated for his injuries at Royal Sussex County Hospital in Brighton.
Two people were arrested shortly afterwards. A 42-year-old man from Worthing on suspicion of committing grievous bodily harm and failing to stop after a road traffic accident, said police, and was bailed until August 22 pending further enquiries.
A 40-year-old Worthing woman was also arrested, but has since been released without charge, police said.
Detectives are appealing for anyone who witnessed the incident – or anyone who has dash cam or CCTV which may have captured it – to report it online or call 101, quoting serial 1073 of 05/06.
You can also contact the independent charity Crimestoppers anonymously on 0800 555 111 or report it online.