The 25-year-old central defender, capped 16 times, could eventually cost Valencia up to 15 million euros with add-ons.

Otamendi has been at Porto since signing from Argentinian side Velez Sarsfield in 2010.

Valencia are way off the pace for a place in either the Europa League or Champions League for next season, currently lying eighth on 28 points, 29 adrift of leaders Atletico Madrid.

Porto are third in their title race, four points behind leaders Benfica, and also went out of the Champions League in the group stage.