[3] Following an unsuccessful spell in Real Madrid's academy,[3] he made his La Liga debut aged 17 with his hometown side Racing de Santander.

[4] Marcos' reputation continued to grow at Atlético Madrid, and he was at the time the country's most expensive signing when FC Barcelona paid 150 million pesetas for his services in 1982.

[5] In his first year he scored six goals in 30 matches in the league, and also an injury time header against Real Madrid in that campaign's Copa del Rey final, which ended with a 2–1 win.

[6] However, Marcos was also one of four Barça players who failed to find the net in the final of the 1985–86 European Cup against FC Steaua București, in a penalty shootout loss, as goalkeeper Helmut Duckadam saved all taken attempts.

In his first experience he led lowly Rayo Vallecano to a first-ever victory over Real Madrid at the Santiago Bernabéu Stadium (2–1),[11] managing Racing[12] and Sevilla FC afterwards (one top-flight promotion with the latter followed by immediate relegation).