The 71-year-old suffered a head wound and a serious leg injury and remains in hospital after the “violent and cowardly” attack.
Police said the man was struck from behind while walking down Mexborough Avenue between 1pm and 1.15pm on Friday.
It is believed the suspect stole money from the victim before making off.
Extra patrols have been put on since the incident.
Detective Sergeant Al Burns of Leeds District CID, said: “Enquiries are ongoing today into what has been a violent and cowardly assault with a weapon on a lone man who was simply going about his business in the street.
“This is being treated as an isolated incident and police patrols have been increased in the area.”
He added: “The victim was been left with a serious leg injury as a result of the attack and I would like to hear from anyone who has information to help us locate the man responsible.
“Anyone who saw the attack, a man in the area carrying a metal bar, or who has any information is asked to contact Leeds District CID on 101.
The suspect is described as around 5ft 9ins, plump with short fair hair and wearing a black jacket.He was carrying a white handkerchief and a silver metal bar.