A Leeds fan was taken to hospital after falling from the stand at Stamford Bridge during their FA Cup fifth-round tie with Chelsea.
The supporter fell from the top tier after Mateo Joseph had opened the scoring for Leeds in the eighth minute.
A London Ambulance Service spokesperson said: “Shortly before 8pm on Wednesday February 28, we received reports that a person had fallen from a height at Chelsea football club in Fulham Road.
“Alongside colleagues from St John Ambulance and doctors from the club, an ambulance crew on scene treated a man before taking him to a London Major trauma centre.”
Leeds said: “Leeds United can confirm an incident involving a Leeds United supporter occurred in the Shed End of Stamford Bridge during the first half of tonight’s FA Cup game.
“The incident is being investigated and is in the hands of the emergency services.”
A police spokesperson said: “Officers, alongside paramedics and staff from Chelsea FC, responded to an injured man in the away end during the match with Leeds United on Wednesday, February 28.
“The man was taken to hospital for treatment. We await an update on his condition. His family has been informed.”