The woman was assaulted between 3.15am and 3.45am on Saturday, May 8, near the roundabout junction between Dumbarton Road and Broomhill Drive – just off the Clydeside Expressway.
Detective Inspector Mark McLennan of the Greater Glasgow Division Public Protection Unit said: "We’re carrying out extensive enquiries to establish the full circumstances of this incident and are appealing to anyone with information which could help to come forward.
"In particular we would be keen to speak to a woman who stopped officers near the roundabout at the time. She left the area without leaving her details and we would be keen to speak further to her as she may have information which is important to our investigation.”
If you have any information you should contact Police Scotland on 101 quoting incident number 2682 of May, 8.