Amorim insists he sees the negativity from the likes of Paul Scholes and Gary Neville as "normal".
Ahead of facing Bournemouth tonight, the Portuguese said: "I think it's normal.
"It's a fact that me as a manager of Manchester United, I think we are underachieving. We should have more points, especially this season. So, I take that naturally.
"Sometimes they don't have all the information and see Manchester United with the standards they lived here, always winning. It's hard for them to see their club in this situation."
Asked if the criticism unsettles him, Amorim says it doesn't.
"No," he added. "Not winning is the issue.
"The problem is that me as a manager, I'm not doing good enough. That is a fact also and I can accept that. The only problem for them is that Manchester United is not winning and is not in the position that it's supposed to be.
"If you are winning, there is no issue."