The victim was attacked with a broken bottle and is in a ‘serious condition’ in hospital.
The attack occurred last night in London at bisexual singer Jessie J’s after-performance party, which was sponsored by phone company Blackberry and held at Pulse nightclub off Southwark street.
The singer finished her set around 11.40pm and the fight broke out in the cloakrooms.
Gay journalist Benjamin Cohen, Channel 4’s technology correspondent, was at the gig.
He told the Daily Telegraph newspaper: ‘Everyone tried to leave at the same time but the organizers weren’t geared up for it and there was a huge rush to get to the cloakroom.
‘People were crying and quite a lot were being sick, whether from the blood or the alcohol.’
A 25-year-old man has been arrested. The 450 concert audience was kept in the club until 1:50am while police launched their investigation.
No charges have been made yet.