West Ham have promised their summer spending is not over.
The club hope to complete the signing of a "young international who represented their country to distinction at the World Cup" this week.
The Hammers' announcement said: "West Ham United are delighted to announce the loan signing of Israel defender Tal Ben Haim and can confirm the club are close to securing another international player.
"Ben Haim is the fourth new face in Avram Grant's squad in what has been a busy summer of arrivals. He is an experienced centre-back with a strong character. He can play across the back four and will provide top-level competition for the club's existing defenders.
"With the ink barely dry on Ben Haim's contract, club officials stepped up their bid to secure a fifth signing this close-season and hope to have the deal finalised within the next 72 hours.
"The potential recruit is a young international, who represented his country to distinction at the 2010 FIFA World Cup."