Dalot has made just seven senior appearances for Porto, however, United were also impressed by his performances in youth team games.
Manchester United's first choice right-back is of course Antonio Valencia, but at 32, he is edging towards the end of his career.
José Diogo Dalot Teixeira, known as Dalot was in October voted as Porto's Young Player of the Year and is rated as one of the best young talents in world football.
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Matteo Darmian, who has been a reserve for Mourinho in both full-back slots, is expected to leave, so Dalot is seen as a replacement for the Italian and as a challenger for Valencia's first-team berth.
Seems like a poor guy can't write scout reports for a few hours without his mentions and DMs being exploded into an insane mess of Diogo Dalot questions. Mourinho is said to be in the market for a left-back and another central midfielder.
Matteo Darmian is set to join Juventus, while Dutch global Daley Blind is unlikely to still be a United player by the start of the new season.
The Spain global has two years left on his deal with the Catalan club and talks over a new deal seem to have stalled.
Cristiano Ronaldo is upset by Manchester United's reluctance to make a move for him in the summer transfer window, according to Don Balon.