#4 Matthijs de Ligt
The second teenage center-back on this list, de Ligt might be among the best defensive prospects in the world. At the age of 18, he has become a regular for both Ajax and the Dutch national team.
Tall, two-footed, a fantastic passer, physical, and very comfortable on the ball, de Ligt has everything it takes to become a Barcelona player. In addition to this, the player himself is open to joining the Spanish giants, with reports saying that he is "keen" on joining a bigger team.
The player's agent has said that he wants to stay at Ajax until the end of the season, so it is likely he'd want to move in the summer window. The Catalan side, as reported by The Week, is expected to make an offer for the center-back in the region of €20 million this summer for a player, who is seen as a potential replacement for Pique.