Police are appealing for witnesses after a 51-year-old man walking in Brougham Road, Worthing, at about 11am on Tuesday September 24, was confronted by a younger man who demanded money near to the junction with Ham Road.
The attacker punched and kicked the victim, who walks with a stick after having a number of strokes, before taking £50 from his wallet and leaving.
The victim, who lives in Worthing, was able to stagger home but is still in pain from the attack.
Detective Constable Kim Clinch said: “Brougham Road is very busy and during the incident a bus and many cars passed by but no one stopped to give the victim any help.
“We are keen to speak to anyone who might have seen what happened but did not realise how serious the attack was at the time.
“This was an unprovoked attack on a vulnerable man and we need to speak to anyone who has any information urgently.”
Anyone with information should call 101 quoting serial 611 of 26 September or the independent charity Crimestoppers anonymously on 0800 555111.