The incident happened on the corner of Ramshill Road and Westbourne Grove, opposite the Ramshill Hotel at 1.30pm on Thursday, September 16, and police are now appealing for a witness.
Officers are appealing to trace a biker who witnessed the assault, which police described as "shocking".
They particularly want to trace the rider of a red sports-style motorbike who was waiting at the traffic lights of the junction when the incident took place, as they may hold vital information.
The rider was wearing a blue and black jacket with a white logo and stripe on the back and a distinctive white helmet with a red stripe through the middle.
Detectives want to speak to any witnesses and drivers who were in the area at the time of the incident, especially those who may have captured dash cam footage.
Any witnesses, or anyone with any information which could assist the investigation are asked to dial 101, select option 1 and speak to the Force Control Room quoting reference number 12210202985.
Information can be passed on anonymously to Crimestoppers on 0800 555 111 or online at www.crimestoppers-uk.org
A 32-year-old man has been arrested in connection with the assault and currently remains in police custody.