The Daily Mail said former World War Two pilot Kenneth Tyrer, 90, died at the weekend, two days after being attacked at Yeovil District Hospital.
His son Bill said: "Somebody has to be accountable for his death."
Yeovil Hospital said in a statement it was "working closely with the police and coroner's office following the death of a patient".
It added: "We are also carrying out our own internal investigation. Our thoughts are with the family at this very difficult time."
The newspaper reported that Mr Tyrer, from Milborne Port in Somerset, had flown Hurricanes and Spitfires on hundreds of missions for the Royal Air Force.
He had been admitted to hospital in May with an infection. He also had dementia, was deaf and going blind.
Bill Tyrer, who lives in Spain, said his father had remained in hospital because he had been too frail to live at home alone. There had been plans for him to move into a care home where his wife lived.
"He should have been safer than he was at home. He was the sort of person I thought was the backbone of Britain. He never complained, he never asked for anything," he said.
"He fought for this country and now we have to fight for him."
A spokesman for Avon and Somerset Police said: "We are investigating the circumstances around the death of a man at Yeovil Hospital. The hospital is helping us with our inquiries."
Police are investigating the death of a man who was reportedly attacked by another patient on a hospital ward.