Miguel Herrera has decided to leave Javier Hernandez out of his Mexico squad so that he can sort out his future.
Sky Sports understands that Dinamo Zagreb striker Duje Cop is attracting interest from clubs across Europe.
Diarra, 31, joined West Ham last summer from Marseille, but picked up a thigh injury in training in September and has played just once for the club.
Diarra, who has 44 caps for France to his name, has spent most of his career in France, most notably in a successful spell at Bordeaux between 2007 and 2011.
Rennes will be the sixth Ligue 1 side Diarra has played for, following Le Havre, Bastia, Lens, Lyon, Bordeaux and Marseille.