The Health and Community Services and Complaints Commissioner looked into the man's case after a complaint from the state's ambulance service about his condition, including concerns he was malnourished.
Premier Steven Marshall said the man's treatment was unacceptable and there was "no doubt we have let this patient down".
"We apologise for that," he said.
"In this situation we have fallen well short of an acceptable standard."
Mr Marshall said the government had accepted all of the commissioner's 13 recommendations and if there was a need for change within the system, that would be put in place.
"We will take action to ensure that this never happens again," the premier told reporters on Monday.
The man was being cared for in a Transition to Home centre operated by the South Australian Department of Human Services, designed for short stays for disabled people until long-term housing is sourced.
The man was transferred to the centre in May last year after spending several months in hospital following a fall at his family home.
Commissioner Grant Davies said his investigation found serious failings in the man's care and ruled that the facility was not appropriate for his needs.
"I am disappointed that the care of a consumer living with a disability is again under scrutiny," Associate Professor Davies said.
"The public summary clearly outlines failings in hygiene, wound care and weight monitoring and how they led to a situation that should have been avoided."
Among his recommendations, Prof Davies urged the department to apologise to the man and his family for the inadequate care he received.
He also called for the Transition to Home service to better assess the care and hygiene needs of its clients, review its eligibility criteria, identify the needs of people as they enter the service and put in place a plan to ensure those needs are met.
Health Minister Stephen Wade said the commissioner's report highlighted the need for the department to have "line of sight" of the medical needs of their clients and not just their personal needs.
"The department of human services completely acknowledges that and is in the process of fixing it," he said.
"The best way to show respect to people when we do let them down is to make sure we take every step possible to make sure it doesn't happen again."
But the state opposition said the man's case was a "shameful indictment upon how this government treats people in its care".
"This is a shocking case and the details from the SA ambulance report on this elderly man are just appalling," Health Spokesman Chris Picton said.
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