[4] On 27 August 2019, after spending the pre-season with the first team, Holsgrove was loaned to Spanish Segunda División B side CD Atlético Baleares on a season-long deal.

[7] He returned to the Royals in July 2020, despite Atlético Baleares attempting to extend his loan deal to cover for the play-offs, as the season was delayed due to the COVID-19 pandemic.

[8] On 10 September 2020, Holsgrove signed a permanent two-year contract with La Liga side RC Celta de Vigo, being initially assigned to the reserves also in the third division.

[9][10] After impressing with the B-side, he made his first team debut on 5 January 2021; after replacing Lautaro De León in the 81st minute, he scored his side's second in a 2–5 Copa del Rey away loss against UD Ibiza.

[11] Holsgrove made his debut in the Spanish top tier on 8 January 2021, replacing Miguel Baeza at half-time in a 0–4 home loss against Villarreal CF.