Frequency of Skilled Nursing Home Visits

Physician sees SNF patients weekly ~ no acute issues, just to check up on them and their chronic conditions. Medicare is paying for these visits.
Concern is that the visits are not "medically necessary".
Physician feels that yes they are; in order to prevent admission to hospital.
Per my understanding, "Medical necessity" includes "visits for the diagnosis and treatment of an illness or injury, or to improve the functioning of a malformed body member"
My feeling if this were a patient that lived at home with chronic conditions, the physician would see them quarterly; so is it really necessary to see them weekly just because they are in an SNF...
Are you able to offer guidance on frequency of SNF/NH visits, etc?
Thank you~