Full name "Jose Diogo Dalot Teixeira", he joined the Porto academy as a nine-year-old in 2008 and broke into the first team during the 2017-18 season under manager Sergio Conceicao.
Porto accept that they have to sell, with the release clause having been met and Dalot's contract expiring next year.
United have moved quickly to sign Dalot amid interest in him from a number of leading clubs throughout Europe, including Juventus, Napoli, Real Madrid and Barcelona.
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.More news: Kilauea Volcano Lava Flow Bears Down on Pahoa Property
Dalot has been described as a "modern full-back who is comfortable in attack" according to the report.
He was part of the Portugal Under-17 side that won the European Championship in 2016 while he also played at the Under-20 World Cup.
It is expected that United will make around five signings this summer, with a raft of players, including probably Marouane Fellaini, leaving as Mourinho revamps his squad.