The 58-year-old was walking towards Allied Irish Bank on West George Street, Glasgow, at about 1.30pm on Monday when he was attacked.
The businessman had just walked past a black parked BMW car when a man who was leaning into the window of the car assaulted him and tried to steal a backpack which contained a substantial amount of cash.
The victim's friend, a 43-year-old man, saw the assault and ran across the street.
He pulled the attacker off the victim and they began fighting in the middle of the road.
The would-be thief then ran down West George Street where he got into the black BMW.
Both men suffered only minor injuries in the incident but were left very shaken. The attacker is described as white, Scottish, about 50, 5ft 11in, with cropped grey hair and a stocky build.