The incident happened in Church Street just before 5.45am today (August 3).
Officers and London Ambulance Service crews attended and found a man injured.
He was taken to hospital where his condition was assessed as not life-threatening.
A second man was arrested nearby on suspicion of grievous bodily harm and possession of an offensive weapon.
He was taken into custody at a south London police station.
A spokesperson for Metropolitan Police said: “Police were called at 5.42am on Thursday, 3 August to reports of a group of men fighting in Church Street, Croydon.
“Officers attended along with the London Ambulance Service.
“A man was taken to hospital with a stab wound to his hand.
“His condition was not life-threatening.
“A second man was arrested nearby on suspicion of grievous bodily harm and possession of an offensive weapon.
“He was taken into custody at a south London police station.
“An investigation is under way and enquiries are ongoing.
“Any witnesses are asked to call 101 quoting CAD 1033/03Aug.”
