Officers have today released an e-fit image of the person they want to speak to about the attempted robbery in the Hyde Park area on Friday, March 16 at around 9.40am.
Police said the victim was walking along an alleyway between Queens Road and Kings Road.
As he reached the end of the alleyway, the culprit was blocking his path and holding a knife, they said.
The victim then ran off and nothing was taken.
Officers want to speak to a man in connection with the offence who is described as black, aged 20-25, of skinny build and with a long slim face.
He was wearing a brown hooded coat and tracksuit bottoms.
Any witnesses or anyone with information about it is asked to call police on 101 quoting crime reference 13180125095.