The 27 year-old striker arrived at the police station, early on Wednesday and was placed in detention, the local prosecutor confirmed to AFP, without giving further information.
Investigators are trying determine the extent to which Benzema was aware of the intimate video featuring Valbuena, which found its way into the hands of blackmailers.
According to the source, Benzema mentioned the sex tape to Valbuena during a meeting of the French team in early October.
It is thought one of Benzema’s relatives was contacted by the suspected blackmailers with a view to involving the footballer in their scheme, the source said.
Police are seeking to determine whether he was teasing Valbuena when he mentioned the tape, or trying to make him pay the blackmailers.
the striker, who was heavily linked with a move to Arsenal in the summer but opted to stay at Real Madrid, missed the game against Paris Saint-Germain on Wednesday, with the club saying that he had picked up an injury with the national team.
Likewise,last month, former Liverpool striker Djibril Cisse was held in police custody in connection to the alleged blackmail case.
The ex-France international was understood to be one of four men under investigation by French police.
Cisse and Valbuena have previously been teammates both at international level for France, as well as at club level for Marseilles between 2007 and 2009, however police conducting the inquiry told French newspaper, Le Figaro, that Cisse was part of their investigation into a plot to extort Valbuena of money.