The 25-year-old defender had been heavily linked with a £17million move to Fulham as he's slipped down the pecking order at the London Stadium. But West Ham have clung on to the Frenchmen as their first-choice centre-backs make long awaited returns from injury.
Kurt Zouma is currently the only fit senior centre-back at the club, with Craig Dawson, Nayef Aguerd and Angelo Ogbonna on their way back from injuries.
West Ham's problems at the back lurch from one crisis to another with Diop now digging his heels in over a move away from the club.
The Irons were forced to play Ben Johnson at centre-back for the 2-0 opening day defeat to Manchester City on Sunday afternoon, leaving many fans asking were Diop was.
Now West Ham manager David Moyes has admitted that Diop is not injured and has not made himself available to play in recent matches.
Moyes said: "No, Issa Diop is not injured at the minute. Issa Diop didn't put himself forward to play in the last couple of games and we will see what happens with that in the next couple of weeks."
Asked if Diop was likely to leave, he added: "I don't know."
Diop posted a cryptic message on his Instagram account on Monday morning, as Fulham reportedly edged closer to sealing a £17million deal.
West Ham suffered as a result and looked there for the taking against Manchester City.
"It was really difficult," said Moyes.
"They played really well. We found it very hard today. It was really difficult tactically to deal with. We couldn't get near them today.
"From our point of view we were resilient, we hung in there and stuck at it.
"But today the talk should be about Manchester City. They played very well. Hopefully we can do better in the weeks and months to come."