According to Joseph Lichtenstein, a medical malpractice attorney in NYC, taking expert advice outside a professional visit won’t put the practitioner liable. For a doctor-patient relationship to be established, as per legalese, the patient allowed the doctor to treat or examine him. Medical records will ideally prove that this relationship was established at the time.
The second is to prove that the practitioner’s actions isn’t standard protocol. Proving breach of the medical standard of care requires an expert witness to testify whether or not the practitioner had deviated from the normal procedure. Without an expert witness, the judge will often dismiss the case despite overwhelming evidence.