Emergency services were called to Elmfield Road in Hyde Park amid reports that a group of men were fighting in the road.
A 57-year-old man was taken to hospital in a critical condition and died several days later.
Onlookers alleged that he had been thrown through a window but South Yorkshire Police have not confirmed this.
A post mortem examination to establish the cause of death was inconclusive and further tests are to be carried out.
Detectives arrested four men - aged 29, 37, 41 and 48-years-old - on suspicion of assault and they have been released on bail pending further enquiries.
Officers are now appealing for any witnesses to the incident, which happened on Sunday, May 14, at 10.30pm, to come forward.
A police spokesperson said: "Enquiries are ongoing into the circumstances surrounding the death of a man in Hyde Park, Doncaster, earlier this month.
"While a post mortem examination has been carried out, the exact cause of death has not yet been determined and further reports and tests have been requested.
"The investigation remains ongoing.
"Anyone with information about the incident is asked to call police on 101 or email [email protected] quoting incident number 1194 of 14 May 2017."