Ramirez has been hotly tipped to shine by football pundits after an impressive spell for Uruguay in the Olympics recently.
He had been expected to join the Reds with the lure of joining international teammates Luis Suarez and Sebastian Coates, but the arrival of winger Oussama Assaidi from Heerenveen yesterday put end to the speculation.
The 21-year-old says he is looking forward to the challenge of playing for the South coast club.
“They believe in me in every way,” he told Corriere dello Sport. “And above all I have said that they are going to grow.
“Southampton is a newly promoted team in the English top flight, but they have the means to stand tall in a few years. And with me they are going to build.
“It’s all very stimulating – even if it is a little strange.”