The victim, who is believed to be in his 40s, was found on Stratford Road, at the junction of Priestley Road in Sparkbrook.
Paramedics treated the man at around 12.50am on Monday and took him to hospital, but he died a short time later.
Three men in their 30s and another man in his 20s have been arrested on suspicion of murder and remain in police custody.
Detective Superintendent Shaun Edwards, from Force CID, said: "We are still trying to piece together what happened in the early hours of this morning.
"We are appealing for anyone who was in or around the area, in particular if anyone has any dash-cam footage that captures the incident, to get in touch.
“Part of Stratford Road has been cordoned off while a thorough forensic search is carried out; with detectives also examining CCTV in the area.”
Anyone with information can call us on 101 quoting log 101 of September 26, or contact the force via live chat at west-midlands.police.uk.
Information can also be passed anonymously to the independent charity Crimestoppers on 0800 555 111.