The central defender’s buyout clause was reportedly triggered by the Saints and the 21-year-old’s arrival at the Premier League club has now been confirmed after all personal agreements were reached.
While he is yet to be capped for the Ghanaian national team, Salisu was one of the most impressive defensive performers in La Liga this season and had attracted interest from clubs further afield.
Premier League transfer news has included speculation on the Ghanaian defender’s future this summer with multiple clubs linked to a deal.
A report last month in Diario AS claimed Rennes had hoped to sign the player but Salisu’s preference was a move to the Premier League as he is a native English speaker, he preferred the style of play and was also offered a more enticing economic package.
“It is a very good feeling to be a Southampton player. I am very happy to be part of the club and I am looking forward to starting here,” Salisu told the club’s official website.
“Southampton is a club with a very rich history in developing young players, so it is a very good club for me to develop my skills and to learn a lot as a young player.
“I know that the team expects a lot from me and I’m going to try to give all I can to help the team.”
Saints boss Ralph Hasenhüttl has said: “This is an important signing for us. Mohammed is a player who fits our profile well. He is young and has a great amount of potential, but he is also someone who has the qualities to come in and help the team as soon as he is up to speed with our way of playing.
“I like what I have seen of him so far in his games with Valladolid. He is strong defensively, he is calm with the ball – something that is important in our team – and he has good speed too.
“I think he will fit in well with us and that this will be a good place for him to develop his game further. We have some good centre-backs here and this will be another strong option for us.”