The unnamed victim was walking along a street in Thuong Tin District's Hong Van Commune at around 5 p.m. when another man, covered from head to toe, came up from behind and slashed the victim's right leg clean off.
Police were soon dispatched and the victim hospitalized.
A representative of Tu Nhien Commune, where the victim lives, said they suspected the incident to be an "act of revenge" as the victim himself was involved in the criminal world, working with gambling rings in Hanoi.
A hunt is on to find the perpetrator.