The incident is said to have taken place at around 7.55am on Tuesday [January 8] in Darenth Avenue, near the junction of Derwent Road.
A man in his 20s told officers he was approached from behind and assaulted.
South East Coast Ambulance Service treated the victim for a puncture wound to his leg. He was taken to a local hospital and later discharged.
Officers are keen to speak to a man who was seen in the area at the time. He is described as white, of medium build and wearing a white t-shirt, grey jogging bottoms and white trainers.
Anyone who witnessed the incident or who has any information is asked to contact Kent Police by calling 01622 604100 quoting reference 08-0252.
Alternatively, you can contact the independent charity Crimestoppers anonymously on 0800 555 111.