Police have released an identikit image of a man they are seeking in relation to the sexual assault of a woman in Dunedin's Ross Creek this week.

Detective Senior Sergeant Kallum Croudis said police were keen to hear from anyone who knew the man.

He said the man was not necessarily linked to the attack, but a woman approached by a man two hours before the attack told police he was wearing similar clothing.

A 23-year-old woman was knocked to the ground, tied up and sexually assaulted about 9.15pm on Monday night.

Det Snr Sgt Croudis said at a press conference this morning officers had talked to a woman who believes she may have been approached by the attacker two hours before the attack.

The man approached the woman on a track in the Ross Creek Reserve but left the area when a dog accompanying the woman came out of the undergrowth nearby.

The woman had provided a description of the man, which had been made into an identikit image.

It also emerged at the conference the offender had used black cable ties to tie up the woman.

The ties were now with Environmental Science and Research Services for forensic analysis.

The attacker was wearing a black balaclava, and police were asking the public to keep an eye out for a discarded balaclava.

Police had also dressed a mannequin in clothing the man was believed to be wearing.