Amorim is playing a second string as he attempts to protect his best players for their Europa League final against Tottenham.
"Manchester United should be able to play in two or three competitions at once without sacrificing something, and they’ve clearly sacrificed the league," the 50-year-old wrote for TNT Sports.
"I don’t like it and I don’t agree with it and I believe there has to be some sort of standards required in a Premier League team.
"It’s almost as if they go into Premier League games and there’s an acceptance that they’re not going to win the game, which is madness. I think the acceptance has come from everyone.
"I think it’s come from the manager even though he won’t admit it. He’s not playing teams to win games of football in the league. I think even fans are thinking let’s get these league games out of the way because the league has been a disaster."