Is refraining from massaging his father's feet considered a sin or an act of disobedience if it causes physical harm to the son?

It is obligatory to obey one's father if he requests an action that benefits him physically, and there is no harm in it to the son, even if it involves a tolerable hardship. For it is necessary to obey parents in matters that do not involve disobedience (to Allah), and if there is benefit for them (the parents) and no harm to the son. The Lord's pleasure lies in the father's pleasure, and His displeasure in his displeasure. And the father is the middle gate of Paradise.