Manager threatening to give negative feedback on relieving letter

Hi, This is Shiva, I have recently submitted my resignation at my current company and since another person in my team had already submitted resignation there is a tough situation at my project. (Only 3 people in my project, 2 in India and one more in USA). The other person left a few days ago and there was a replacement found for him only a couple of weeks before he left hence he didn't have to give much knowledge transition to him and no one questioned him much. But now since I am also leaving in another month they have asked me to give the complete knowledge transfer in a very short span. The replacement resource is apparently a fresher and hence it's quite hard for him to grab on. My manager is threatening that he will provide negative feedback because of incomplete knowledge transfer. How can this be fair when the other person who left earlier was not questioned at all, and the new person is infact the replacement for the one who left and not me, for my replacement is yet to be recruited. Please help.