He says the incident was "not related to the officer's role as a police employee''.
An internal investigation will also be undertaken, and police say they won't comment further on the officer's involvement "at this stage''.
Police have interviewed the victim and made preliminary enquiries with Mainland Football.
Senior Sergeant Paul Merrett says police hope to speak to other witnesses in the coming days.
"We are appealing for anybody who has seen what occurred to contact us as soon as possible so that they can be interviewed,'' he says.
Any witnesses or people with information about the incident are asked to contact Mr Merrett on 03 3741760.