פירוש על עבודה זרה 55:10

Generally speaking it is prohibited for a non-Jew to heal a Jew if the wound is serious enough that we could transgress Shabbat for it (such as scurvy). The fear is that the non-Jew will surreptitiously kill him. But if the person being healed is an important man like R. Yohanan, then we are not afraid that the non-Jew will kill him.