The defender, 20, has had a slow start to his Juve career.
"I'm still not at my best, I know that," he said after Netherlands' 2-1 win in Belarus yesterday.
“The more I play, the more I'll get there. What I can do is keep working hard, doing my best and learning from my teammates.
“At Ajax I felt a sense of invincibility. Now I feel less so, but it's natural. I have a little less confidence than I did last season.
“I'm at a new club, with a new style of play and new teammates. For me, it's all new. It's less familiar than at Ajax, but I'm getting better and better."