The Frenchman has reportedly agreed a four-year deal in France.
They claim the French international will return to his homeland on a free transfer after FIFA finally cleared him to play for another team. He will sign a four-year deal at the club.
In the winter West Ham tried to sign Diarra on a free transfer. The former Portsmouth man had been released by Russian side Lokomotiv Moscow after a contractual disagreement.
The Frenchman spoke of the failed move and FIFA in an interview with L'Equipe at the time of the first failed transfer. He revealed that deals to join both West Ham and Inter Milan had been stopped by FIFA after Lokomotiv complained, suggesting he was still their player.
Now the summer is here he is free to go where he wishes and back home appears to be his preferred destination.
This comes despite reports this week in The Daily Mail that West Ham remained keen on the player, who trained with the club for several months in 2015.
However it is becoming increasingly apparent that Diarra will continue his footballing career back in his French homeland for the time being.