A man was left with 'life-changing injuries' after he was attacked as he queued for a toilet during an event at Bowlers Exhibition Centre.
The assault happened during a fully-licenced music event at the centre on Longbridge Road, Stretford, last Sunday.
Police said there were more than 400 people present at the time.
Greater Manchester Police said the victim - a 26-year-old man - was queuing to use a toilet when he was 'subjected to an unprovoked assault and left with potentially life-changing injuries'.
He was taken to hospital where he was confirmed to have a bleed to the brain, facial fractures and nerve damage to an eye, police said.
He was also treated for loss of hearing in one ear.
Police said the man, who hasn't been named, remains in hospital for ongoing treatment and is in a 'stable' condition.
It happened between 6pm and 6.30pm on Sunday, September 6.
Bowlers said it was a Kaluki music night run as part of the Social Avenue series of events and was fully-licenced by Trafford council.
Socially-distanced pods were in use.
A spokesman for the centre said security were at the scene of the assault within seconds and paramedics were on site.
He said it was an 'isolated incident' and no other incidents were reported.
Police said they now want to speak to anyone present at the event and who may have any mobile phone footage.
Detective Sergeant Tim Flint, of GMP’s Trafford division, said: "The injuries inflicted to the victim here are absolutely awful and it is of paramount importance that we identify the person responsible for this and hold them to account for this vicious assault.
"We know there were over 400 people at this event and therefore I am confident that there will be witnesses out there who saw the incident itself, the preceding moments, or its aftermath and can help us with our enquiries.
"Anyone with video evidence from the evening of the incident is of particular interest to our investigation and I encourage anyone who was there to check their phones for any content they may have from around the time of the assault."
Call police on 0161 856 7573, quoting incident number 732 of 12/09/2020, or Crimestoppers on 0800 555 111.
