Absent injuries, and with the benefit of seeing his performance in the Newcastle game, it appear to me that it only really makes sense playing Warnock as a left sided midfielder in a wing back formation. In the 3 man backline, his defensive duties are limited and there is less chance of him being exposed. At the same time he is not required to be a "winger" type of left sided midfielder, which requires more skill and pace.
While I admire his spirit, he is too limited at present to be a regular, confidence inspiring part of a title challenging back 4.