Mackay emerged through local Deportivo de La Coruña's youth ranks, but never managed any first-team appearances, only now and then being summoned for trainings. In his first year as a professional, he was loaned to third level sides, AD Ceuta and AD Universidad de Oviedo, being released in 2007 and joining another side in that category, UD Vecindario.
In 2008, Mackay returned to Galicia, joining lowly SD Ciudad de Santiago, also in level three, and immerse in a severe financial crisis. In the following summer, he moved to SD Ponferradina, yet in Segunda B.
Personal
Although born and brought up in Spain, Mackay has Scottish ancestry, which would enable him to play for the national team.