Officers investigating the mystery incident say they are trying to speak to witnesses after the young man, only 23 years old, collapsed close to the entrance of Bassetlaw District General Hospital and subsequently died.
Nottinghamshire Police said: "At about 9.25pm on May 31, a 23-year- old man collapsed close to the entrance of the hospital. He had been dropped off to make a visit to the maternity ward.
"Between the drop off and his collapse, the man suffered a catastrophic brain injury and died."
Officers investigating his death are currently treating it as unexplained and are keen to hear from anyone who saw anything unusual or suspicious who may have been in the vicinity of the hospital and the One Stop convenience store between 8pm and 9.30pm on the night of May 31.
The man is described as white, about 5ft 8ins tall with collar length hair. He was wearing glasses and had on a light blue hooded top, a black t-shirt with a white and brown picture on the front, blue jeans and olive green trainers.
DI Andy Bateman who is leading the investigation said: “We do not know how this man came to suffer such a critical head injury. At this point, we know that he was fit and well when he was dropped off near the hospital.
“This is a really busy area of Worksop, particularly the One Stop shop so if you were in thE area at the times stated, please cast your mind back to whether you noticed anything at all that seemed unusual.”
Police are urgently appealing for anyone who saw the man or anything out of the ordinary to contact 101 quoting incident 864 of 31 May.