According to Portuguese sports daily, O Jogo, Arsenal have fully scouted and have even begun negotiations for the 19-year-old forward, who has yet to complete a full match this his debut season.
However, despite not completing a full match, Castro has scored a total of seven goals in 20 league contests and showed the pace and goal-scoring prowess garnering praise and comparison's to Spain's all-time leading scorer, David Villa.
Castro began with the Real Oviedo youth system before joining the Sporting Gijon reserves, where he would go on to make his professional debut on 10 September 2014, eight days after signing his first, first team contract.
He would make his Segunda debut two weeks later and scored his first goal two weeks after that, showing his potential right from the start.
Castro has two years remaining on his current deal and his price-tag will be a drop in the bucket for an Arsenal side who will buy Castro as "one for the future" joining fellow forwards Yaya Sonogo, Joel Campbell, Chuba Akpom and Serge Gnabry in the same category.
Castro has represented the Spanish U-21 team once, making his only appearance for his country in 2014.