	De Tomás was loaned to Rayo Vallecano on 1 September 2017. He was the second-highest scorer of the season with 24 goals, including hat-tricks in victories over Lorca FC, Cultural y Deportiva Leonesa and CF Reus Deportiu, as the club from Vallecas won the league and were promoted back to the top flight; this haul was a season record for any player in its history, and he was also named Segunda División Player of the Month in February and April 2018.