The France international, who had made just four Premier League appearances for the Hammers, has returned to full training and hopes to feature for the club against Chelsea
The 32-year-old picked up the injury in a 2-1 Capital One Cup win over Cheltenham Town on August 27 and it was initially feared that he would have to sit out the entire season.
The France international has recovered surprisingly quickly, though, and was able to play 90 minutes in a friendly against Gillingham on Tuesday.
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"I am happy to now be doing my job, playing football, and my recovery has been amazingly quick," Diarra told the club's official website.
"I am surprised, like everybody, but we've taken our time and worked hard together and my knee is steady and I can play.
"I played 90 minutes in the game on Tuesday against Gillingham and I think this was my last test. Now, I think I am available for the first team and hopefully I will train hard to have a chance to play with West Ham.
"I am not feeling 100 per cent just yet, but my knee is feeling stable and stronger. With every training session I will get better and I am happy to be playing because it was eight hard weeks.
"I was very unlucky because I did a good pre-season, but football is like that. I must accept my injury and I have worked hard to come back. Now I'm on the pitch and I try to do my best and am available for the team now.
"I will train hard every day to try to play in the Premier League. Maybe I will be involved against Chelsea - I hope so. I hope I will be ready, but it is up to the manager."