The Spanish attacker struggled to make an impact at the Vicente Calderon side last term and will be looking to get his career back on track in Portugal
The Portuguese giants were keen to add an extra striker to their squad amid ongoing reports that Jackson Martinez could be on his way out this summer and they have now found their man in Adrian.
The 26-year-old underwent a medical on Saturday and has signed a contract with Porto until June 2019, containing a minimum fee release clause of €60 million.
Adrian came through the ranks of the Oviedo youth academy and signed for Deportivo La Coruna in the summer of 2006. He enjoyed loan spells at Alaves and Malaga before eventually joining Atletico in 2011.
The versatile attacker impressed in his first two seasons at the Vicente Calderon side, yet lost his starting berth last term and will now be looking to get his career back on track at Porto.
Adrian is Porto's sixth signing of the summer transfer window after the previous acquisition of Oliver Torres, Daniel Opare, Ricardo, Evandro, Sami.