The 68-year-old man had been cycling home from work when he was suddenly assaulted by a younger man walking two dogs.
The thug, who was also in the company of a woman, grabbed the senior citizen off his bike and punched him before fleeing the scene.
The pensioner had to be taken to hospital by police where he was treated for cuts and bruises and later released.
The incident took place on the Holburn Street footbridge in Aberdeen around 6.30pm on July 2.
Police are keen to speak to anyone who may recognise the man who carried out the assault.
He is described as about 5ft 8ins tall and of stocky build with short brown hair. He was wearing a blue t-shirt and black shorts.
The assailant was in the company of a blonde haired female and they were walking two dogs, one of which was believed to be a Jack Russell and the other was a slighter larger dog.
Constable Sean Gulland of the Nigg Community Policing Team said: “This was an unprovoked attack on an innocent member of the public and we are extremely keen to identify the person responsible as soon as possible.
“We are keen to hear from anyone who may have witnessed this incident or who recognises the description of the male assailant or indeed anyone who recognises the descriptions of the dogs and their owners.”
Anyone with information is asked to contact Police Scotland on 101 or Crimestoppers on 0800 555 111.