[2] Óscar made his senior debut on 19 August 2017, starting and being booked in a 1–2 home loss against CF Rayo Majadahonda.

[4] Óscar made his first-team debut on 28 November 2017, starting in a 2–2 home draw against CF Fuenlabrada, for the season's Copa del Rey.

[1] On 13 August 2018, Óscar was loaned to La Liga side CD Leganés for the season, being handed the number 27 jersey.

Óscar scored his first goal in the top tier on 26 September 2018, netting the winner in a 2–1 home win over FC Barcelona.

[14] After representing Spain at under-17, under-19, under-20 and under-21 levels, Óscar received his first senior call-up on 20 August 2020, for two UEFA Nations League fixtures against Germany and Ukraine.