Officers were called to reports of a man who had threated a woman with a knife in Camberwell Road at 3.45am on September 14.
While police were in the communal area of the property, a man fell from a third-floor window.
The man was taken to hospital with life-threatening injuries where he remains.
His next of kin are aware.
There were no other injuries and no arrests following the incident.
A spokesperson for the Metropolitan Police said: “Police were called to a residential address on Camberwell Road, Southwark, at 3.45am on Sunday (September 14) to reports of a man who had threatened a woman with a knife.
“Officers attended and, while they were in the communal area of the property, a man in his 20s fell from a third-floor window.
“Officers were not present in the same room when he fell. Officers administered first aid and CPR, and the London Ambulance Service and London’s Air Ambulance were called and attended.
“The man was taken to hospital with life-threatening injuries, where he remains. His next of kin are aware.
“No-one else were injured during the incident. There have been no arrests. Enquiries continue.”
