Dalot has made just seven senior appearances for Porto, however, United were also impressed by his performances in youth team games.
Dalot has been capped by Portugal at every age group from U15 to U21 level and made his first team debut for Porto in a 6-0 away win over Lusitano G.C in October of a year ago.
Porto accept that they have to sell, with the release clause having been met and Dalot's contract expiring next year.
The 19-year-old, who is a natural right-back but can also play on the left, has been followed extensively by United in recent months as they look for a long-term solution in their defensive ranks. In this picture, FC Porto's defender Diogo Dalot from Portugal attends FC Porto Gala Dragoes de Ouro 2016 - 2017 at Dragao Caixa in Porto, Portugal, Oct. 25, 2017.
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.
Matteo Darmian was brought in a backup for Valencia, but the Italian failed to settle in the Premier League and is now expected to leave in the summer and join Juventus in his homeland.
Dalot will compete with Antonio Valencia for the right-back slot at Old Trafford.
However, the Portuguese is now closing on a move to Manchester United and according to Portuguese daily O Jogo, his representatives have communicated his decision to Porto. Mourinho is said to be in the market for a left-back and another central midfielder.