Police had said they were keeping an 'open mind' when the 49-year-old man was found in Common End Lane in Lepton, Huddersfield, on Saturday.
Now the force has confirmed that the man died in Leeds General Infirmary yesterday evening.
Detective Inspector Lee Donnelly, of Kirklees CID, said: “Although we still do not have a complete picture as to the circumstances, at this stage, we are not treating it as suspicious.
“A forensic post mortem will now take place to further establish the cause of death and assist in unravelling the full nature of this incident."
He said officers were supporting the man's family at this difficult time and continuing to develop a chronology of events.
“Our CCTV enquiries have allowed us to track some of his movements prior to the incident." said Det Insp Donnelly.
“It is important, however, that we can fill in the gaps of the timeline that led to him sustaining these serious injuries.
“I would ask that anyone who has any information, however significant you may believe it to be, to come forward.”
Contact Kirklees CID via the non-emergency number 101, quoting reference 390 of January 20.