Singer Jessie J spoke of her shock on Thursday after a man was left fighting for life following a bottle attack at a celebrity-packed party.
A 25-year-old suspect was being questioned by police on suspicion of slashing the victim's neck at the event thrown by smartphone company BlackBerry.
Brit-award winning singer Jessie J had been performing at the party before the bloody brawl.
She tweeted today of her concern for the 37-year-old victim, described as being in a critical condition.
The singer said: "My thoughts are with the person who was seriously injured last night at the BlackBerry BBM party. So sad. I really hope they are OK."
The victim was allegedly attacked inside Pulse underground nightclub in Southwark, central London, just after midnight.
A Scotland Yard spokesman said: "It appears he was injured with a bottle.
"The man suffered a neck injury. He was taken by ambulance to an east London hospital where his condition is understood to be critical.
"One man has been arrested and remains in custody at a south London police station."
The party was attended by journalists, celebrities including rapper Wretch 32 and stars of The Only Way Is Essex and BlackBerry competition winners.
Photographs posted online following the incident seemed to show pools of blood on the floor near the club's bar.
BlackBerry said in a statement: "A serious incident occurred at our BlackBerry event... Our first concern is the wellbeing of the injured guest.
"We are doing all we can to assist police with their inquiries and are unable to provide further comment at this time."