A report by state investigators said nurses failed to follow sanitary guidelines, equipment was poorly maintained, and walls and chairs were spotted with blood, the Los Angeles Times reported Monday.
In a surprise check in November, inspectors also found equipment that was rusted or held together with tape, the newspaper said.
Regulators have warned the findings could jeopardize government funding for the center that serves about 120 patients.
In a letter to the center Feb. 10, the California Department of Public Health said the facility had 90 days to submit a plan of correction or the center would lose its Medicare funding.
After the inspection, the center's staff was retrained and a new medical director and nurse manager appointed, UCI spokesman John Murray said.
A plan of correction UCI officials submitted to regulators Friday said equipment has been repaired or replaced in advance of an upgrade scheduled to be completed next year.
"We appreciate the seriousness of the issues raised and believe that you will find our response and accomplishments to date to be comprehensive," Dr. Alpesh Amin, head of the medical school's department of medicine, said in a letter to regulators.