The right-back is only 19 but with a release clause of £17.4m, United are ready to pounce - according to reports in both Portugal and England.
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A naturally right-footed player, Dalot has shown his versatility by also playing on the left side throughout his Porto career.
Not many fans will have heard of the 19-year-old, he only broke into the Porto first team in February.
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.
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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.
Dalot is primarily a right-back but can also play at left-back, another problem area for Mourinho.
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Brett Connolly and Nicklas Backstrom scored 42 seconds apart in the first period to put the Capitals ahead 2-1. Ovechkin (12 goals, 22 points) carried them against Tampa Bay, supported by playoff scoring leader Kuznetsov.
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.