According to Sky Italia's Gianluca Di Marzio, West Ham have yet to reach an agreement with Monaco over the transfer of Aymen Abdennour.
The Hammers have been busy this summer, bringing in Darren Randolph, Pedro Obiang and Dimitri Payet to their squad, whilst also appointing Slaven Bilic as their new manager.
More reinforcements are needed, but Sky Italia journalist Gianluca Di Marzio reports that the Hammers have yet to close a deal for Monaco star Abdennour.
The Tunisian international, 25, has become a star in France during spells with Toulouse and now Monaco, with his impressive displays under Leonardo Jardim now triggering interest.
However, the report states that West Ham were on the verge of striking a shock deal to sign Abdennour - but have yet to reach an agreement with Monaco.
That leaves West Ham open to being hijacked, with the report suggesting that AC Milan are now ready to make a late bid to try and take him to the San Siro.
How important is signing a new centre back?
West Ham once again saw Winston Reid impress last season, whilst James Tomkins exceeded expectations to produce a decent season in the heart of the West Ham defence.
Yet, when both players were ruled out injured, West Ham were left with very few options, resorting to playing James Collins and midfielder Cheikhou Kouyate in defence.
That can't happen again, so bringing in another centre back - whether it's Abdennour or another player - is imperative for Bilic and the West Ham hierarchy.