The Frenchman moved to the London Stadium in a deal worth £21.9 million from French side Toulouse, and his new manager believes that player will be an exciting addition to the Premier League.
The Chilean, who won the Premier League while in charge of Man City, told his new club's website:
"Issa is a defender with great talent and character. He is only 21, but he has already established himself as a key player over a period of time with Toulouse,
"We believe he has defensive qualities that will be well suited to the Premier League - pace, power and a sharp concentration - and I also feel he will complement the other central defenders we have.
"We know that many other top clubs in England and Europe were keen to sign him, so it was important that we moved quickly to complete the deal."
The France U-21 international was in Toulouse's youth system, and had indeed attracted interest from the likes of Marseille, Sevilla and RB Leipzig.
The East London club were also quick in their signing of Polish international Lukasz Fabianski, who signed a three year contract following a switch from recently relegated Swansea City.
"We believe he has a number of good years ahead of him - hopefully his best - and there is no doubt that he will give us excellent competition for the number one spot.
"It is important, as a Premier League club, to have strong goalkeepers who can push each other and we have that dynamic with Lukasz and Adrian now."
These two singings followed on from the announcement that Ryan Frederiks had arrived on a free from Fulham, suggesting that West Ham are wanting a big change among their defensive ranks,