Sergio Martínez Montero (born 15 May 2007) is a Spanish professional footballer who plays as a defensive midfielder for Primera Federación club Real Madrid B.
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Club career
Born in Laredo, Cantabria, Martínez joined Racing de Santander's youth sides for the Alevín squad, from hometown side CD Laredo. In October 2024, while still a youth, he began training with the first team.
Martínez made his senior debut with the reserves on 6 April 2025, coming on as a late substitute for Pipi Nakai in a 2–1 Segunda Federación home win over CD Numancia. He signed a professional three-year contract in the summer, and featured with the main squad in the pre-season.
Martínez made his professional debut on 16 August 2025, replacing fellow youth graduate Íñigo Sainz-Maza in a 3–1 Segunda División home win over CD Castellón. On 14 November, he renewed his contract with the club until 2029, and featured in 13 matches overall during the season as they achieved promotion as champions.
Martínez made his La Liga debut on 16 August 2026, starting and scoring his team's second in a 2–2 home draw against Villarreal CF.
On 31 August 2026, Martínez signed for Real Madrid B after the club activated his €3 million release clause.
Career statistics
Club
As of match played 23 August 2026
Honours
Racing Santander
Segunda División: 2025–26