The French international, who joined the Hammers last summer, failed to make much of an impact at Upton Park last season and was sent on loan to Rennes in January where he made ten appearances.
However the holding midfielder had been a key player for Allardyce in pre-season and appeared to have forced his way into the first team squad with two appearances already this season before being stretched off against Cheltenham in midweek.
The 32 year old may have played his final game for the Hammers however as Allardyce fears his season may be over with the terrible injury and his contract is up at the end of the season.
“Alou Diarra got injured the other night and is not involved in the squad,” Allardyce said.
“It’s more serious than we expected and it looks like an ACL reconstruction, unfortunately.
“That will probably finish his season, that is a big blow to us in squad terms. He was hoping to forge his way into the side this season but, obviously with the injury, now that won’t be the case.”
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