The 44-year-old victim was found with fatal injuries on the A38 Bristol Road South in Northfield, on the southern outskirts of Birmingham, just after 5am on July 23.
Despite being treated by paramedics he passed away at the scene.
West Midlands Police has said a post-mortem will be carried out to confirm how the man died, while investigators and local officers speak to people in the area, and examine evidence including CCTV footage.
As of 12pm on Friday, Bristol Road South remains closed at the junction of Bodenham Road and Chelston Road.
The force has asked potential witnesses to come forward, saying: "If you saw what happened or recorded the incident on your phone, CCTV or dashcam, please speak to us. The easiest way to do that is to get in touch via live chat at west-midlands.police.uk or call 101 anytime.
"To remain 100% anonymous please call Crimestoppers on 0800 555 111. Please quote log number 585 of 23/07/21."