Ligue 1 club Rennes had been in negotiations to the sign the player but he is said to have always had a preference for a move to England.
Salisu is said to prefer a move to the Saints for three key reasons – he is more comfortable with speaking English than French, the glamour of playing in the Premier League and a superior financial offer with greater stability.
Premier League transfer news has included speculation on the Ghanaian defender’s future this summer with multiple clubs linked to a deal.
The central defender’s contract at Valladolid runs through until 2022 having been penned back in May, while he is yet to be capped for the Ghanaian national team.
He is viewed as a rising star by the club but is also seen as still having a great deal of room for improvement so may view his next move as a ‘stepping stone’.
Valladolid have already secured the long-term replacement for Salisu having signed defender Javi Sanchez from Real Madrid.