De Ligt worked with United head coach Erik ten Hag when they were both at Ajax.
While they achieved success in the Eredivisie, De Ligt is hoping their relationship can bear fruit in the Premier League as well.
"Yeah obviously (he was) a really important part because he knows me really well, I know him really well," De Ligt told club media.
"He made me captain also at Ajax.
"Also at my time at Ajax he gave me a lot of confidence, he gave me a lot of motivation to try to lead the team."
"He's really demanding, I think," the Netherlands international added.
"He demands, every day, every moment of the training session, he demands a lot.
"Not only on the training pitch, but also outside; how you behave, how you take care of your body, how you rest, how you sleep. And he's really into discipline.
"That suits really well with the way I see being a professional footballer."