Manchester United have prioritised Jurrien Timber from Ajax as their number one defensive target.
The centre-half, who can also play as a right-back, emerged at Ajax under current United coach Erik ten Hag.
According to the Manchester Evening News, United are hopeful of luring Timber to the Premier League.
However, they also have a backup option i nthe form of Portuguese defender David Carmo from Braga.
Carmo is 22 and was close to joining Liverpool midway through last season.
United are also assessing Villarreal's Pau Torres, but he is thought to be an outside option.