The department, which provides medical imaging such as MRI and CT scans, had 40% too few radiologists, the International Accreditation of New Zealand (IANZ) said.
Te Whatu Ora Health New Zealand (HNZ) Southern told the Otago Daily Times there was no nuclear medicine-trained radiologist on site — one of four factors behind the bad rating.
Interim hospital and specialist services leader Hamish Brown said HNZ Southern was finalising a contract for oversight by a private provider.
This was expected to be confirmed shortly, he said.
Radiologist and medical imaging technologist vacancies were also a factor.
"These workforces are in high demand in both the public and private sector across Aotearoa New Zealand and internationally.
"We continue to actively recruit."
IANZ also noted the digital subtraction angiography equipment, a combination of X-ray equipment and high-speed image-processing equipment, was due to be replaced, he said.
"Te Whatu Ora Southern had already purchased replacement equipment and it is expected to be completed in the 2024 calendar year."
Some electrical compliance testing was overdue, but this had now been remedied.
Dunedin Hospital was among five hospitals with radiology departments recently classed as high risk by IANZ, as reported by RNZ last week.
They joined a further four departments deemed as bad or worse on the IANZ August risk register to almost double the number on the risk register compared with last October.
The risk table said the hospital was "40% down on budgeted FTE radiologists".
Mr Brown said there was a 35% shortage in July.
The additional comments section of the risk table noted there was a "potential accommodation problem with [the] new hospital build delayed".
The risk table said IANZ would be monitoring carefully because of the "ongoing resourcing depletion".
Mr Brown said a potential accommodation problem was not referred to in the assessment report provided by IANZ following the review visit in June.
"Population growth has been considered and factored into to the new Dunedin hospital design.
"There will be radiology services in both the outpatient and inpatient buildings."
Southland Hospital, which operated for years without IANZ accreditation, was listed as "withdrawn".
IANZ said the hospital was the appropriate organisation to comment on the potential accommodation problem and other issues and did not answer questions asked by the ODT.
HNZ Southern did not respond to further questions by deadline.