The 24-year-old was discovered in Wallacewell Road in the Balornock area of Glasgow at about 1am on Saturday.
He suffered serious head and facial injuries and is said to be in a stable condition in Glasgow Royal Infirmary.
A man with a dark jacket was seen running away from the scene into a lane next to 231 Wallacewell Road, police said.
Detectives have launched an investigation and are appealing for anyone with information to contact them
Officers want to trace members of the public shown to be in the area on CCTV, particularly a man who was walking a dog at around the same time.
Detective Constable Peter Chatham said: "At this time, we don't know exactly what happened to the victim. We know members of the public tried to help him and contacted emergency services.
"We are trying to piece together the man's movements and I am appealing to anyone who was in the area at the time and to local residents living in that street to contact us."
Anyone with information is asked to contact Police Scotland on 101 or Crimestoppers on 0800 555 111.