The reports further say Salisu signed a four-year deal with the Saints for a fee of £10.9 after his release clause was triggered.
Mohammed Salisu on his debut Spanish La Liga season has been one of the best performers in the league.
After the end of the 2019/2020 season, he made into the list of the breakthrough team of the season as well as the La Liga U-21 team of the season.
Salisu also emerged as the U-21 defender with most clearances in the top five European leagues.
His stellar display attracted offers from several clubs for his signature.
Mohammed Salisu joined the youth ranks of Real Valladolid in 2017 from African Talent Academy.
The defender after one season with the youth was promoted to the senior team where he has since made his mark in the La Liga