Police called at about 5pm to reports of a man stabbed close to Plumstead Railway Station.
Officers attended and the 20-year-old man was taken to hospital by the London Ambulance Service. He has since been discharged.
Officers have since established that the man was assaulted by two males on Plumstead Road at the junction with Walmer Terrace, SE18.
A search of the area led to the discovery of a BB gun. Enquiries remain ongoing to establish whether this is linked to the assault.
There have been no arrests.
Anyone with information is asked to call police via 101 quoting reference CAD 4383/31Dec23.
To remain anonymous, please contact the independent charity Crimestoppers on 0800 555 111.
