Box Hill Sexual Offences and Child Abuse Investigation Team detectives are investigating a sexual assault in Blackburn last month.
Police have been told a 19-year-old woman was out running on Whitehorse Road when an unknown man approached her about 11.10am on Monday, 26 August.
He sexually assaulted her as she attempted to pass him, then fled the scene on foot.
The woman was not physically injured during the incident.
Investigators have released a digital composite image of a man they believe may be able to assist with their enquiries.
He is described as being of slim build with brown eyes with dark curly hair and was carrying a red basketball.
Anyone who witnessed the incident, has dashcam/CCTV footage or information is urged to contact Crime Stoppers on 1800 333 000 or make a report online at www.crimestoppersvic.com.au
