Manchester United are expected to sign Porto right-back Diogo Dalot after activating the 20million euro (£17.44million) release clause in his contract.

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.

It is expected to be a busy summer at Old Trafford with a number of deals mooted but, surprisingly, Dalot is due to be the first signing. United are also in the market for another full-back, a left-back, to strengthen in that area also.

Dalot has already agreed personal terms with United with the highly-rated Portugal Under-21 international expected to push captain Antonio Valencia hard for a place in the first-team.

The 19-year-old only broke into the Porto first-team this season and played out-of-position at left-back during Porto’s Champions League tie away to Liverpool. He has still only made a handful of first-team appearances, however, but is regarded as having great potential.