A 52-year-old man is in a critical condition after being attacked while at a work Christmas party.
Dave Baker, from Solihull, suffered a fractured skull in the assault in Birmingham city centre at around 3am on Sunday.
Four men in their 20s who were arrested after the attack outside O Bar in Broad Street have been released on police bail pending further inquiries.
In a statement issued through West Midlands Police, Mr Baker's son Matt, 22, said: "My dad was just enjoying a Christmas do with his mates.
"It should have been a good night out but has ended with him in hospital with a bleed on the brain.
"I want whoever who did this to him to be found and brought to justice as soon as possible. The police need more witnesses, so I'm appealing for anyone who was there to please call them and tell them what you saw."
Anyone with information is urged to contact Pc Ian Leech on 101 or call Crimestoppers anonymously on 0800 555111.