Two people were taken to hospital after a fight in Union Street early on Sunday morning.
The Metropolitan Police and the London Ambulance Service were called at 6.13am on Sunday morning.
"Two men were taken to a south London hospital, a 24-year-old with a suspected head injury who remains there currently for assessment, and a 21-year-old who had minor injuries," said a Scotland Yard spokeswoman.
"A quantity of cash and an Oyster card were also stolen."
Officers from Southwark CID are investigating.