RCD Espanyol appointed the little-known Diaz to replace Benito Joanet in January 1990.
[1] Diaz would lead Espanyol to the 1989–90 Segunda División play-offs, where the club won promotion following a victory over CD Málaga.
[2] In June 2001 Juanjo was named as manager of second-division side CD Badajoz.
That October, however, he was relieved of his duties after winning only two points out of a possible 27.
[3] He died in Terrassa, Catalonia, at the age of 68, following a long illness.