The Dutchman joined in the summer from Bayern Munich and will compete for a starting spot.
When all are fit, De Ligt will face competition from Harry Maguire, Lisandro Martinez, and Leny Yoro for a starting spot.
"You can't do it with 11 players," the former Bayern man told United club media.
"You need, actually, almost a minimum of like two good players in every position.
"Then it's about competition, and I think this competition makes everybody else a bigger player because you need to show every day that you are the best at your position, that you can help the team."
He added: "We have a lot of really talented young players. We have also the age group of, I think, 22 to 28. We have a lot of also really good, experienced players.
"I think that if you can blend this together, this will be a really good mix."