Lens face being relegated to Ligue 2 at the end of this season regardless of their final position in the table after a court ruling regarding the club's finances on Thursday.
The Administrative Court of Besancon decided that Lens' promotion to the top flight last term summer was invalid. Sochaux, who finished 18th in Ligue 1 in that campaign and were relegated, had brought the case.
The northern club's rise to Ligue 1 had twice been rejected by French football's financial watchdog, the DNCG, due to the club's lack of financial stability before eventually being ratified by the French Football Federation (FFF) just days before the start of the 2014-15 season.
The FFF, who had two months to appeal against Thursday's decision, almost immediately announced it would be contesting the ruling via press release on its official website.
"I'm annoyed," Lens coach Antoine Kombouare, who had refused to take charge of training sessions last summer until the club's promotion was validated, told media at a news conference on Thursday.
"Sochaux make me laugh. They were relegated because they were bad. The reality for Sochaux is that they are in Ligue 2 and are fighting to get back up. We're fighting to stay up.
"I'm only focusing on the pitch. I have fun with my players. That's the only way to protect ourselves. Of course the court's decision concerns me. But I have to keep behaving in the same way with my players."
Despite the best efforts of president Gervais Martel and the promises of Azerbaijani owner Hafiz Mammadov that funds would be forthcoming, the club was banned from bringing in players by the DNCG in either of this season's transfer windows.
Lens are currently second-from-bottom of Ligue 1, thereby occupying one of the French top-flight's three relegation spots, but Kombouare's side are only two points from safety.
Sochaux's request to be automatically returned to Ligue 1 next seasons has been deferred. They are currently in fifth place in French football's second tier, just a point off the promotion places.