Joaquín Martínez Gauna (born 9 July 2003), commonly known as Oso, is a Spanish professional footballer who plays for Sevilla Atlético. Mainly a left-back, he can also play as a left winger. Career Born in Torrevieja, Alicante, Valencian Community, Oso began his career with Algorfa CF, and subsequently represented Kelme CF and Real Murcia CF before joining Málaga CF's youth sides in 2018. He made his senior debut with the latter's reserves on 12 October 2021, playing the last 26 minutes of a 1–1 Tercera División RFEF home draw against CD Alhaurino. Oso scored his first senior goal on 9 April 2022, netting Atlético Malagueño's winner in a 3–2 home success over UD San Pedro. On 13 July 2022, he signed a three-year contract with Sevilla FC, being initially a member of the B-team in Segunda Federación. Converted into a left-back at Sevilla Atlético, Oso made his first team debut with the Andalusians on 6 December 2023, coming on as a late substitute for Manu Bueno in a 2–0 away win over Atlético Astorga FC, for the season's Copa del Rey. The following 23 February, he renewed his link until 2027. Regularly used in the B-team afterwards, Oso made his professional – and La Liga – debut on 7 December 2025, starting in a 1–1 away draw against Valencia CF.