Lucas made his official debut for the Rome club in a 3–2 win over league champions Juventus in the Supercoppa Italiana, on 13 August. His first goal for the club was in a 2–3 defeat to Zulte Waregem in the final group game of the UEFA Europa League. On 28 February 2018, Lucas missed a penalty during the penalty shootout in Lazio's match against Milan in the semi-finals of the Coppa Italia; which Lazio eventually lost 4–5.