With F.C. Barcelona, he was a 3 time finalist in the European Champions Cup (Euroleague), twice the Saporta Cup winner, once the Korać Cup holder, 7 times the Spanish national league champion, and 10 times the Spanish Cup winner. His 54 points scored in a game against Joventut Badalona, in the early 80's, counts among his most memorable performances, and is the 2nd best scoring record ever in the Spanish League. Ranko Žeravica, was the one who gave him the opportunity to play for Barcelona's first team, in 1979. In 1973, he made his debut with CN Helios, in the Spanish third division. He was named by the Best European Player of the 80's, L’Equipe.
San Epifanio, known by almost everyone simply as, "Epi", grew up in Zaragoza, and began to play in his native city, but the local club, C.N. Helios Zaragoza, rejected him. In 1974, F.C. Barcelona signed his older brother, Herminio, to a contract. Herminio insisted that Juan would join him at the club, and so the two moved to Barcelona.
With F.C. Barcelona, Juan quickly improved his skills, and became a member of the Spanish junior national team.
In 1977, he joined the first team of Barcelona, and quickly became the leading man in Barcelona's successful team of the 80's, which finally broke the long-lived dominance of Real Madrid, after a prolonged period; together with players such as, Ignacio Solozábal, Juan de la Cruz, Audie Norris, and others.
In the same year he debuted with F.C. Barcelona, he also made his first appearance with the Spanish national team. He appeared in a total of 239 games, giving him the all-time lead in national team appearances for Spain.