Dalot, who has already agreed personal terms, has made only a handful of first-team appearances for Porto after breaking into their team last season when he featured against Liverpool in the Champions League.
Mourinho lacks faith in United's right-back options beyond Valencia, who is 32 and needs back-up for his position to allow him to be rotated. Interest in Diogo Dalot has been present for a while now, with FC Porto rejecting multiple bids below the player's €20 million release clause.
The Telegraph write: "United are also in the market for another full-back, a left-back, to strengthen in that area also".
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.
Not many fans will have heard of the 19-year-old, he only broke into the Porto first team in February.
Contact between the clubs has been made and it seems only a matter of time before the deal is completed.
The player's agent has criticized the club after they failed to live up to their promise of handing the defender a new contract.
And according to Goal, United are hopeful of landing Porto right-back Dalot before the end of the week.
"[When] Raul Sanllehi [now at Arsenal] was still at the club when they told us not to worry, that they were going to call us to renew", Alba's agent Vicente Fores said, as quoted by the Mirror.