A man has undergone surgery for a blood clot on the brain after being found injured in a side street in Windsor.
The 23-year-old from London was discovered by a police officer on Sunday at 0330 GMT in a service road near a taxi rank on Goswell Hill.
Police said he had suffered injuries to his head and eye.
He was taken to Wexham Park Hospital before being transferred to Oxford's John Radcliffe Hospital where his condition is improving.
Det Con Jon Groenen, of Thames Valley Police, said: "We're currently trying to piece together how this man came to sustain such serious injuries.
"It is unclear whether he has fallen, been assaulted, or even been involved in a road traffic collision.
"We know that he had been in Vanilla's nightclub on Saturday evening and would appeal for anyone who may have any information, or seen a man matching his description, to get in touch immediately."
The man is white, 5ft 10ins tall, of slim build, with fair hair. He was wearing a light coloured blue and white checked shirt.