The 25-year-old was seriously injured and his car was stolen after he pulled over on East Bawtry Road, Whiston, at around 10.50pm yesterday.
South Yorkshire Police said the man, who was travelling alone in a white Mercedes, briefly pulled over close to the junction with Lease Gate Road.
As he got out of his car it was reported that he was approached by a group of unknown men and attacked with a with metal weapon.
The attackers, who got out of a dark-coloured vehicle, then left the scene in the victim’s Mercedes.
The victim was taken to hospital, where he remains in a serious but stable condition this afternoon.
In a statement, South Yorkshire Police said: “The victim was taken to hospital with a life changing arm injury. He remains in a serious but stable condition.
“An investigation is under way and officers are currently following a number of lines of enquiry including reviewing CCTV and house-to-house visits.”
Anyone with information should call 101 and quote incident 985 of April 7 or Crimestoppers, anonymously, on 0800 555 111.