De Ligt was speaking ahead of today's trip to Liverpool.
He told manutd.com: "I think everybody can understand that it's a difficult period, not only for the players, I think also for the fans, for the staff, for everybody involved in the club.
"I think a club of the size of Manchester United shouldn't be in 14th place, I think, at the moment. So yeah, we know that, we know it's tough for us, for everybody, but the only thing that we can do and control is the work we do on the pitch.
"Today we had a good session, we trained really hard, and this way, I think we hope to solve this period and to make it a better period for us, for ourselves."
On doubts about Amorim's system, De Ligt said: "I think people from the outside are looking into it too much.
"If you saw our matches this season, it was also with (Erik) ten Hag, we build up always with a three, with Diogo Dalot as an inverted midfielder.
"So, we built up with a three like we do now. We defended high up the pitch with one full-back, so we defended also with a three. With (Ruud) van Nistelrooy it was also the same, we built up with a three.
"I can understand that people are always watching and looking to find a solution but the only thing we can do is to control our performances, control our way of working, and that's what we try to do."
On Liverpool, the Dutchman insisted: "You always have to believe.
"Maybe from the outside, it's now easy to think: 'Oh, United is going to Liverpool, Liverpool (in) great form, United maybe in not so good form, oh, it's done.'
"But in football, it's never like that. So we believe in that and we try to work as hard as possible to get a result there."