A woman needed 19 stitches after being hit across the face by a stranger in Norbury.
The unknown attacker is thought to have assaulted two women during the evening on Monday April 20.
A 34-year old woman got off the route 109 bus at Standford Road junction with London Road on the way to meet a friend when the man attacked her.
Police do not know if the man used a weapon or not.
An 18-year-old women was also assaulted earlier that evening but did not need hospital treatment.
Police are appealing for witnesses.
The suspect is described as a black man, aged 18-years and about 155cm in height. He is of slim build, with short hair and a long face.
The motive of the attack is unclear as no property was taken from the victim.
Anyone with information is asked to contact the CID at Croydon Police on 020 8649 0258 or to remain anonymous Crimestoppers 0800 555 111
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