The doctor's lawyer said neither the doctor nor others in her office knew who filled in the incorrect diabetes diagnosis.
Rivas also said the doctor played no role in the official certification form sent to Medicare, although records show she billed Medicare for the review of the form and its plan of care.
"The records provided by ABC News do not support any allegations of fraud. It would be irresponsible journalism to air a story on Medicare/Medicaid fraud using this referral as an example when there is clearly no evidence of fraud," he added in a letter to ABC News.
ABC News ended the undercover investigation before any medical supplies or equipment could be billed to Medicare based on the false diagnosis.