The 52-year-old grabbed at the blade as the hooded thief demanded he hand over his money and valuables in Great Union Road at around 9.45 pm yesterday.
He was left bleeding in the road as the attacker ran off empty-handed towards Windsor Street.
Detectives said this morning that the victim had suffered cuts to his hand and a tendon injury and was still receiving hospital treatment.
The robber is described as being aged in his late teens or early 20s, a white European and between 5ft and 5ft 7in tall.
He was wearing a brown or grey anorak-style jacket with a hood.