The 21-year-old has signed a four-year contract and joins the Saints for a reported club-record fee of £12million.
Southampton manager Nigel Adkins said: “A lot of hard work has gone in from the football club with a lot of negotiations behind the scenes to get this deal done.
“Great credit to everyone because we have a young, exciting talent joining us who is one of the best around.
“The chairman has gone and backed this deal big-time with the financial outlay, and what we have got is one of the most exciting prospects in world football coming to St Mary’s.
“There is a lot of ambition here and we are all delighted that Gaston is going to come and join us.”
What is your opinion? Feel free to discuss the article under. You have to comment by using your Facebook profile. Be fair and have respect for other people and opinions!
The start of the 2017-18 Premier League season is just around the corner and is shaping up to be one of the most competitive yet.
As always it is the so called “big clubs” that have splashed the most cash in the transfer window so far this summer. Manchester United or City? Arsenal or Tottenham? Who are the winners and losers of the transfer window so far?