However, he insists United are not suffering from instability.
"The first thing I want to say is that, since the first day, I felt great support from the ownership," said Amorim ahead of their Europa League tie against Viktoria Plzen.
"From Omar (Berrada, chief executive), from Dan also, from Jason (Wilcox, technical director). Dan was part of that, and I really felt support from Dan also.
"But this is football and sometimes these things happens. It happens with players, with coaches.
"I know that it's not the best situation but the important thing is we continue in our way. The path is really clear for everybody and I think this can happen in football."
Asked about instability, Amorim added: "I don't think so. I've felt since day one the support from everybody, so one person leaving doesn't change nothing.
"Of course, it's a bad situation, because we are talking about a human being, a professional, that supports us as a team.
"But I think the most important thing is that your vision is really clear and that vision doesn't change if only one person leaves."
On the need to sell before buying, Amorim said: "No, I'm really focused on (managing) to see my players and to understand my players. I think that is one of the problems of the club.
"We have to focus on what we have. We have to focus on the academy and also have a clear profile when you get the players, so it's a lot of details you have to manage.
"You can see at set-pieces, sometimes you look at our team and we are a small team compared to others.
"Every detail counts and we have to be very clear first in the profiles, arrange all the process, and then go to that phase of buying and selling players."