I'm a masters student in mathematics and I gave a seminar talk about my main result. A professor in the audience gave a one sentence comment during my talk. It is an important comment about my work, which I didn't think of myself, and I added it to my paper (but did not yet send it for publication), including an acknowledgement to the aforementioned professor, specifying that this is "his" comment.
Is it unethical if I don't contact him to tell him I acknowledge him in the paper? For personal reasons, I would not like to be in any contact with this specific professor (because of his highly inappropriate behavior towards me in previous interactions, on which I did not take action because I have no proof.).