The incident occurred in Green Wrythe Lane at around 8.50pm on December 15.
Officers from the Metropolitan Police were dispatched after being alerted by the London Ambulance Service to reports of an alleged assault.
At the scene, paramedics treated a 45-year-old man for severe head injuries.
He was taken to hospital where his condition has since been confirmed as non-life changing.
A cordon remains in place whilst initial enquiries get underway.
There have been no arrests.
A Metropolitan Police spokesperson said: “The London Ambulance Service called police to the scene of an alleged assault in Green Wrythe Lane, Carshalton at around 20:50hrs on Monday, 15 December.
“Paramedics treated a 45-year-old man for severe head injuries, before transferring him to hospital where his condition was confirmed as non-life-changing.
“No arrests have been made at this time. A crime scene remains in place while officers conduct initial inquiries.”
Anyone with information relating to the incident is urged to contact the Met via 101, quoting 7284/15Dec.
