Bayindir, making his Premier League debut against Newcastle, gave away possession for the Magpies’ fourth goal.
Amorim says Onana, a £44m signing in 2023, “deserves” to return to the starting XI.
“When I made that decision I talked with Andre and that is important for me to explain to the player to understand what I am thinking,” added Amorim.
“Sometimes the player is saying one thing and I understand it’s a different thing, sometimes it is my feeling as a coach that can make my decision more than what they are saying to me. They want to show they are really confident and I can feel the other way. So I have the conversation but it is my decision in the end.”
Amorim was joined at his press conference by defender Harry Maguire, who backed Onana to recover his form.
“Andre has proven in the past that he is an excellent goalkeeper,” said Maguire.
“In a career you always have spells when you go up and down – it is about how you build yourself up. You have times when you feel everything is going against you.
“He is a big personality and big character and will want to show everyone what he is all about. Playing in front of Andre is great.”