A Leeds United fan was taken to hospital after falling from the top tier at Stamford Bridge while celebrating a goal against Chelsea.
The two sides met in the FA Cup fifth round on Wednesday night, with Chelsea coming out on top in the final minute of the game to win 3-2.
But it was the Yorkshire club that opened the scoring through Mateo Joseph in the eighth minute in west London.
Amid the celebrations in the away end – where visiting teams are given a bigger-than-usual allocation in the FA Cup – Leeds United confirmed an “incident” took place.
“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,” it said in a statement.
“The incident is being investigated and is in the hands of the emergency services.”
Chelsea issued an identical statement.
Footage shared on social media appears to show a Leeds fan fall from the top tier of the corner of the Shed End.
The person seen in the footage falls onto empty seats, with no other Leeds fans near enough to be in danger.
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A spokesperson for the Met Police told the Yorkshire Evening Post the supporter’s family has been informed.
“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, 28 February,” the force said.
“The man was taken to hospital for treatment. We await an update on his condition. His family has been informed.”
Leeds United and Chelsea have a historical rivalry, which is seen by some as an embodiment of the north-south divide.