Casal became a professional tennis player in 1981 and won his first ATP double title in 1983. In total he won 47 double tournaments, mostly with his compatriot Emilio Sánchez . In the individual, however, he could only win one tournament.
Between 1985 and 1987 he was in the Davis Cup against Killy Sánchez Germany each Boris Becker defeat in singles. So he only beat Boris Becker, who was still almost unknown in March 1985, and the reigning (and already two-time) Wimbledon winner in March 1987. From 1981 to 1995 Casal played 48 games for the Spanish Davis Cup team with a record of 31:17 wins (doubles 19: 9).