As part of a freshly-launched murder inquiry, Derbyshire Constabulary has released this CCTV image of a man, woman and child who may have witnessed the alleged incident.
Police are urging them to come forward and speak to officers.
The man, woman and child were seen in High Street, Staveley, at around the time of the alleged assault on Wednesday evening, June 21, according to police.
The alleged assault happened between 6.15pm and 6.30pm, in the Beechers Brook pub, on High Street.
An ambulance was called and the injured man was taken to Sheffield’s Northern General Hospital.
The alleged assault victim has been named by police as Peter Matts, 69, of Staveley.
Police confirmed Mr Matts has since died in hospital and a murder inquiry has been launched.
Jason Knowland, 45, of High Street, Staveley, has already been charged with assault occasioning grievous bodily harm after the incident.
He is due to appear at Derby Crown Court on Monday, July 24.
Anyone with information regarding the alleged assault or CCTV footage is asked to contact Detective Sergeant Adam Gascoigne on 101 quoting reference number 17000262050.
A message can also be sent online by visiting the Contact Us section of the Derbyshire Constabulary website www.derbyshire.police.uk/Contact-Us.
Those with information can also call Crimestoppers in confidence on 0800 555 111.