	On 3 July 2019, De Tomás signed a five-year contract with Portuguese champions S.L. Benfica on a €20 million transfer fee. He debuted for the club as a starter in the 5–0 thrashing of crosstown rivals Sporting CP in the Supertaça Cândido de Oliveira on 4 August. He scored his first competitive goal for the side in a 1‒3 loss at FC Zenit Saint Petersburg in the group stage of the UEFA Champions League, as a substitute; UEFA ordered his shirt to say his legal surname for that match, while he habitually wore his initials instead. 