Police were called to Southwark Street at about 2.27am on Sunday 5 November following what the Metropolitan Police described as "reports of a fight involving a number of individuals".
"Officers attended and located two males with serious injuries. One suffering with stab wounds and the other suffering with a head injury," said a Met spokeswoman. "They were both taken to hospital for treatment."
According to the Met, the stab victim remains in a life-threatening condition. The second male's injuries have been assessed as not life threatening.
Southwark Bridge Road and Marshalsea Road were closed during the day on Sunday whilst a forensic examination took place.
No arrests have been made and officers are continuing to investigate.