The 32-year-old was released by the Cottagers at the end of last season and has not figured for the club since suffering a knee injury in December 2012.
Diarra is yet to return to full match sharpness and remains in the free-agent pool as a result.
He has, however, been training with Fulham over the summer and could be handed a new deal at Craven Cottage if he can convince Martin Jol that he is deserving of a place in his squad.
"He is doing a lot of ball work and the warm-ups with us," the Dutch coach told the Fulham Chronicle of the former Real Madrid enforcer.
"He needs another three or four weeks before playing games with us or the reserves and then we will make a decision on him."
Meanwhile, Jol has revealed that he will look to send promising forward Chris David out on loan this season in an effort to get the 20-year-old important game time.
He said of a player who moved to England from FC Twente in January: "He's a very talented left-footer. He looks good but he needs games.
"Abroad they go into the first team at 18 or 19, but you don't see that in England.
"They go on loan, like (Alex) Kacaniklic, come back and be better. That is my idea with the youngsters, to try to find clubs for them."