He was wearing a hooded black leather or vinyl jacket, black pants and dark coloured sneakers.
The incident appeared to have occurred as a result of a dispute over payment, Mr Collins said.
"Police believe this is an isolated incident related to the transaction, and there is no indication of any connection to other assaults on sex workers in the central city over recent months.''
Police were appealing for any information would could lead to the identification of the man in the image.
They were also interested in hearing from members of the public who may have been in the area around the time of the incident, or who had seen any suspicious activity in the vicinity.
Anyone with information is asked to contact Christchurch police on (03) 363 7400.
Alternatively, information can be provided anonymously through Crimestoppers on 0800 555 111.