Benzema, 33, is suspected of helping a group of alleged blackmailers approach Valbuena in an attempt to extort money. Four other men are also on trial.
The case cost both Benzema and 37-year-old Valbuena their places in the French national team, though Benzema was restored to the squad for this year's European Championship.
The case centres on the role that Benzema is suspected of playing in the murky affair six years ago, which started when Valbuena handed his smartphone to Axel Angot, a man connected to footballing circles in the southern port city of Marseille, with the request to transfer its contents to a new device.
Angot, now on trial for breach of trust, came across sexually explicit footage on the phone involving Valbuena.
Prosecutors says he then explored ways -- together with a friend, Mustapha Zouaoui -- to approach Valbuena and threaten publication of the footage unless he paid them.
