Emergency services were called to Baylis Road, by the entrance of Waterloo Millennium Green, yesterday (October 8) at 7.46pm.
Medics arrived in less than four minutes, and a man was treated for a head injury.
He was then taken to hospital as a priority.
A police cordon has been in place since the attack, with the park still shut off today (October 9).
Tape is surrounding the entrance on Baylis Road and officers are at the scene.
The Metropolitan Police has been approached for more information.
A London Ambulance Service spokesperson said: “We were called at 7.46pm on Wednesday 8 October to reports of a stabbing on Baylis Road, SE1.
“We sent an ambulance crew and a clinical team manager to the scene.
“Our first paramedic arrived in less than four minutes.
“We treated a man for a head injury and took him to hospital as a priority.”
