Southampton have announced that Juanmi has left the club to join La Liga side Real Sociedad.
The 23-year-old only joined Southampton last summer, moving to St Mary's in a £5.25m deal from Malaga.
However, he failed to make a single Premier League start all season and has now moved back to Spain on a five-year deal for an undisclosed fee.
Juanmi made just two starts in all competitions for the Saints and was mostly used as a substitute, making a further 17 appearances off the bench.
Sociedad finished ninth in the Spanish top flight last season.