He played mainly for Real Sociedad (five years) and Barcelona (three) in his professional career, achieving La Liga totals of 273 matches and 42 goals in ten seasons.

With the first, he was instrumental in back-to-back La Liga conquests (averaging 32 games and five goals in those seasons and not starting only once), and won 19 of his 20 caps for Spain in the process; his debut came on 24 September 1980 in a friendly with Hungary (2–2), in Budapest.

[3] In 1982–83, having retired from the national team following the unsuccessful home World Cup campaign, Alonso joined Barcelona,[4] being used relatively little during most of his spell.

He won the league in his final year, but only appeared twice, eventually retiring in 1988 with Barça neighbours Sabadell, helping the club achieve promotion from Segunda División in his first season and scoring 12 goals – a career-best – in his second, as the modest Catalans ranked 17th after the first 34 matches, but eventually managed to avoid a drop after finishing third in their relegation group in the second stage.

In 2000, after an unsuccessful spell at Hércules (second division, relegation),[7] he had a chance to coach Real Sociedad but only lasted ten games, retiring from the sport subsequently.