On 27 June 2017, after returning from the UEFA European Under-21 Championship, Fernandes joined Sporting CP on a five years deal, for a reported fee of €8.5 million plus bonuses. He scored four goals in his first five Primeira Liga games, including a brace in a 5–0 away win against Vitória de Guimarães. Fernandes' first appearance in the UEFA Champions League group stage was on 12 September, where he put the visitors 3–0 ahead in the 43rd minute of an eventual 3–2 win at Olympiacos FC. He finished his first season with 16 goals across all competitions, second only to Bas Dost.