The 25-year-old has joined Middlesbrough on loan until the end of the season.
Ramirez becomes the second new signing of the January transfer window for Boro, following the arrival of Kike Sola.
Ramirez joined Southampton in a £12million deal from Italian side Bologna in the summer of 2012.
CONFIRMED | @gasramirez10 joins #Boro from @SouthamptonFC – https://t.co/b62m1R0Ggw pic.twitter.com/dg8Dwi1v7n
— Middlesbrough FC (@Boro) January 26, 2016