Fabricio Coloccini has re-affirmed his commitment to Newcastle amid fresh speculation that he wants to leave.
Paris St Germain forward Ezequiel Lavezzi has not ruled out a move away from the big-spending club.
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.