The incident between a pedestrian and a bus happened in George Street just before 1.10pm today (October 5).
Officers and London Ambulance Service crews attended and found a man injured.
He was taken to hospital for treatment where his condition is currently unknown.
A crime scene has been put in place following the incident.
A spokesperson for Metropolitan Police said: “Police were called to George Street, Croydon, at 1.09pm on Saturday, October 5, to reports of a collision between a bus and a pedestrian.
“Officers attended along with paramedics from London Ambulance Service.
“A man in his 40s was found injured. He has been taken to hospital.
“A scene has been put in place.”