Diarra joined the Hammers from Marseille for £2million in August 2012 - but struggled to make an impact at Upton Park and spent the last half of the 2012/13 season on loan with Rennes.
He suffered a serious injury in their Capital One Cup second-round victory over Cheltenham earlier this season, with the France international being stretchered off in the 34th minute with an anterior cruciate ligament problem.
Sam Allardyce feared at the time that Diarra would be out for the season - but he is back to full fitness and played in the 2-1 defeat at Fulham, albeit at centre-back rather than his preferred midfield position.
That was a rare outing for the 32-year-old, who is desperate to depart Upton Park in January but is not too keen on a return to France.
Diarra, who has played for Le Havre, Bastia, Lens, Lyon and Bordeaux - where he scored 11 goals in 132 appearances - told L'Equipe: "When I talk with other Frenchmen, I would have loved to experience the same as them - but there is a whole world between us. The great excitement of the Premier League - I am not experiencing it at all.
"Since the very first day people wanted me to accept that I am second choice. I'm in a dead end.
"It was a bad career choice and I need a real challenge.
"A January departure? Yes it is very likely. To France? I've explored it all."
Diarra added: "The fact I was back from broken knee ligaments after six weeks without having surgery? Some people could hardly believe it.
"Anyway my situation has not changed. I am not fooled. I quickly understood he (Allardyce) didn't rely on me, as I am again confined to the bench."