The Portugal Under-21 international is expected to undergo a medical with Manchester United next week once they finalise his fee with Porto.
Dalot has been receiving treatment for a meniscus injury while United have been negotiating over his £17.4m release clause.
United want a right back to compete with Antonio Valencia, who is 33 and needs constant treatment on a knee injury.
Dalot is a right-back that can also play left back. He broke into Porto’s first team in February in that position and played in his club’s 0-0 Champions League draw at Liverpool.
He helped Portugal win the 2016 UEFA European Under-17 Championship, scoring twice in five games in Azerbaijan including once in the final against Spain.
United expect to offset the deal with outcast Matteo Darmian’s £11.5m sale to Serie A champions Juventus.