Élisabeth Berthet has published an article titled Application du critère des contestations sérieuses dans le cadre d'un référé brevet ("Application of the criterion of serious questions with regard to a patent in suit") in the July 2015 issue of Propriété Industrielle (pp. 16-17). Dr. Berhet argues that a 2014 judgment of the Cour de cassation, Société Ausio MPEG Inc. v. Société Electro dépôt France, Cass. com., 21 Oct. 2014, No. 13-15,435, has resolved the question of whether under L 615-3 of the Code of Intellectual Property as revised in 2007 a person opposing a preliminary injunction must demonstrate, as under previous law, only "serious questions" (contestations sérieuses) regarding infringement or validity of the patent in suit, or instead "manifest nullity" (la nullité manifeste). In relevant part, the pre-2007 version of this statute provided that a court could award a preliminary injunction only "if the substantive proceedings appear well founded" ("si l'action au fond apparaît"), while the new law reads "Toute personne ayant qualité pour agir en contrefaçon peut saisir en référé la juridiction civile compétente afin de voir ordonner . . . toute mesure destinée à prévenir une atteinte imminente aux droits conférés par le titre ou à empêcher la poursuite d'actes argués de contrefaçon ("Any person with a right to assert a claim for infringement may commence an emergency civil proceeding to obtain . . . any measure intended to prevent an imminent harm to the rights conferred by this act or to cease alleged acts of infringement") (my translation, see blog post here; see also discussion in my book at pp. 242-43). Apparently, under the old law the consensus was that a "serious question" was sufficient to defeat the application for a preliminary injunction; and while most courts and commentators believed that this standard still applied under the new law, according to Dr. Berthet there was a minority view that the new law required a stronger showing on the part of the defendant, namely "manifest nullity."
Anyway, the issue was raised in the case referenced above, and while the Cour de cassation did not expressly state that the Cour d'appel had erred in requiring a showing of manifest nullity, it did (in affirming the appellate court's judgment in favor of the applicant) state that the evidence suggested a probable infringement (contrefaçon vraisemblable) of the patent and that it did not make out a serious case of invalidity (aucune cause sérieuse d'annulation). Dr. Berthet reads this as indicating that the Cour de cassation approves the use of the old "serious questions" standard, which she believes balances the interests of the parties.