United have moved quickly amid interest in Dalot from clubs including Juventus, Napoli, Real Madrid and Barcelona.
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 have been left surprised by Dalot's decision and the club could have reconsidered selling Pereira to Leicester had they known the youngster would want to leave.
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The statement added. "This is obviously contrary to the consensus reached between the two sides in Washington not long ago". The US will request that tariffs and taxes between the two countries be reciprocal in nature and value.
Dalot has been described as a modern full-back who is comfortable in attack, with good delivery and an eye for goal, and has operated in midfield.
The teenager was a member the Portugal Under-16 side who won the European Championship two years ago and the Under-17 team who won the corresponding competition 12 months ago.
Manchester United's first choice right-back is of course Antonio Valencia, but at 32, he is edging towards the end of his career. Dalot is expected to be given first-team opportunities, with Mourinho clearing out players such as Matteo Darmian and Daley Blind to make way for further recruits.
An announcement is due within the next few days as manager Jose Mourinho steps up his efforts to strengthen United's defence this summer as he attempts to close the gap with Manchester City after a trophyless campaign. Mourinho is said to be in the market for a left-back and another central midfielder.