A product of La Liga powerhouse Real Madrid's youth system, Madrid-born Gallego made a quick impression with the first team, appearing in 26 matches in his first year and being a midfield mainstay the following seasons as he totalled 250 top-division matches with the conquest of, among others, four leagues, two Copa del Rey and consecutive UEFA Cups (1985–86); blessed with physical and technical ability alike, he could operate with equal efficiency as sweeper.

[3] In the 1986–87 campaign, Gallego contributed 37 appearances and two goals (more than 3,000 minutes) as Real Madrid won the national championship,[4] also reaching the semi-finals of the domestic cup.

[5] On 15 March 1987, however, he unluckily landed on Miguel de Andrés' knee, and the Athletic Bilbao player ended his career after that game, a 2–1 win at the San Mamés Stadium.

[6] Following a brief spell with Italy's Udinese Calcio, Gallego returned to Spain and the Spanish capital, spending one season with Rayo Vallecano in the Segunda División and achieving promotion.

[7][8] Gallego played 42 times for Spain,[9] his debut coming in a friendly prior to the impending FIFA World Cup on home soil, a 24 February 1982 victory over Scotland: after replacing FC Barcelona's Víctor Muñoz in the second half, he closed the score at 3–0.