Beckham signed a five-month deal with the French side on transfer deadline day after leaving LA Galaxy at the end of the MLS season last year.
The 37-year-old revealed that he was donating all of his salary to a local children's charity, though that didn't stop some parts of the media pouring scorn on the move.
Fernandez, who enjoyed two spells at the club in the mid 1990s and early 2000s, admits that Beckham's arrival does have a commercial aspect to it, given his high profile.
However, he has backed the former Manchester United and Real Madrid man to make a significant impact on the pitch.
"To see David Beckham arrive is enormous," he told RMC."This is both a sporting and a marketing coup. He can contribute to the group both in training and on the pitch because of his experience.
"He has outstanding quality in his technique and passing."