A reveller, 20, suffered life-threatening head injuries during a Cheetham Hill rave in the early hours of Saturday morning.
The Salford man was taken to Hope Hospital and is still in a critical condition after being found injured at the rave in a disused warehouse on Derby Street.
And officers are investigating whether an assault took place or if the man was injured accidentally.
Detective Sergeant David Elson said: “A man is in hospital with serious head injuries and it is vital we understand exactly what happened to him.
“He has a bad injury to the back of his head so it is possible he was assaulted by someone in the rave. It’s also possible that he fell over and there is an accidental cause.”
Police responded to another unrelated incident at the rave and arrived at about 3am.
But they were approached by several partygoers, who informed them a man had been injured.
They are now appealing for information from other revellers to clear up the cause of the man’s mystery injuries.
“There were between 200 and 300 people there in the early hours of Saturday morning and officers did speak to a number of people on the night,” said Detective Sergeant David Elson.
“However, if you were there and have any information that can help us then please get in touch.
“In particular, I would like to hear from anyone who may have mobile phone footage of the incident that led up to this man being injured.”
Anyone with information is asked to call police on 0161 856 9325 or Crimestoppers on 0800 555 111.
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