The France Under-21 international enjoyed a superb campaign in Ligue 1 last season and was also wanted by Everton and Sevilla
West Ham United have confirmed the signing of Toulouse captain Issa Diop on a five-year deal.
The France Under-21 international becomes Manuel Pellegrini’s second signing of the season after Ryan Fredericks joined on a free transfer from Fulham.
The fee, which was not disclosed by the club, makes him the club’s record transfer fee signing ahead of Marko Arnautovic.
It is believed he had his medical yesterday, with Pellegrini keen to do business quickly.
He told the West Ham United website: “I am very happy to sign for such a historic, English club, and I hope to show my best here.
“I am a very ambitious player and West Ham is a very ambitious club, as we’ve seen with the appointment of the new coach. I hope to help the team win lots of games and make the fans happy.”
West Ham United Director of Football Mario Husillos added: “Issa is a player with fantastic potential who has already shown great quality at such a young age.
“It is a measure of his character and maturity that he was named captain of Toulouse at just 20 years of age, having already established himself in their team as a teenager.
“He has represented France at every youth level up to Under-21 and we believe that he is now ready to make the next step in his career by moving to the Premier League with West Ham United.”
Everton and Sevilla were reportedly interested in the 6”4 centre-half, but it is the Hammers who have snapped him up.
A deal for Swansea City goalkeeper Lukasz Fabianski is also expected to be announced imminently.
The 33-year-old was an unused substitute as Poland slipped to a 2-1 defeat to Senegal in the Group H World Cup game on Tuesday.
According to the Evening Standard, the former Arsenal shot-stopper will sign a three-year deal at the London Stadium after a £7 million fee was agreed.