Amorim has been repeatedly questioned by a host of former United players turned pundits including Scholes, Butt, Gary Neville and Roy Keane.
Scholes, who won 11 Premier League titles during Sir Alex Ferguson's reign as manager, has been particularly fierce in his criticism.
The former midfielder has said that Amorim is not "the right man" and doesn't "get the club."
In response, Amorim said the opinions of ex-stars are "normal," but added they don't understand everything that's happening behind the scenes at Old Trafford.
"I think it's normal," said Amorim. "I think 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 they see Manchester United with the standards that they lived here, always winning. So it's hard for them to see their club in this situation."
Amorim has endured a difficult first year as United manager, winning just 14 of 42 Premier League since his appointment in November 2024.
Scholes has also taken aim at the 40-year-old's style of play -- implementing a back three instead of a back four -- and his treatment of academy graduate Kobbie Mainoo, but Amorim believes all the criticism from former players would disappear if the team won games more regularly.
"I think not winning is the issue," said Amorim. "Of course you can point to a lot of things and they point to a lot of things that we need to improve, but the big issue is not winning. If I'm winning I can go to the games on a horse, arrive there, playing with just two defenders and everything will be fine.
"The problem is that me as a manager I'm not doing good enough and that is a fact also and I can accept that. So that is the only problem. For them it's that Manchester United is not winning and is not in the position that it's supposed to be."
