Halakhah zu Mischlej 9:9

And all that we have written applies even if he said about him only that he is not wise in worldly matters. How much more so, if he said about one whom the people of the city thought to be wise in Torah, that he is not so wise, and that he knows but little in Torah, and through this they come to think less of him. Certainly this is in the category of lashon hara, even if true, since his intent is not for benefit but only to lower his friend in the esteem of the hearers. For through this, on whichever level he stands, this can cause him harm, or, in any event, distress. I will provide two illustrations. If one says about the city Rabbi before the people of the city that he is not very wise in Torah, but that he knows a little of the halachic rulings that are needed in practice — even if this be true, it is absolute lashon hara according to the Torah. For by this, he completely lowers his honor and undermines his very livelihood, and decreases thereby the honor of the Torah and the fulfillment of its mitzvoth (as mentioned in section 2). The same applies if he says the like about one who was recently married in the city. For certainly his honor will fall in the end in the eyes of his in-laws and of the members of his household when it becomes known to them that he is of little consequence in the city. And there is no greater harm and pain than this and the like. It is difficult for me to illustrate everything, but, "Give to the wise and he will wax yet wiser" (Mishlei 9:9). For I have come only to arouse, and the wise man will understand all by himself. And know also that the same applies if he says about a worker that he is not a good worker. This, too, is absolute lashon hara, for here, too, all the aforementioned considerations apply. (And if in this and all the other instances that we have spoken of, his intent is not to demean, but only to derive some benefit, this will be discussed, the L–rd willing, in Principle IX of the laws of rechiluth.)