Here is a typical list of standards that should all be met:
(1) a strong likelihood of success on the merits, (2) the possibility of irreparable injury to plaintiff if preliminary relief is not granted, (3) a balance of hardships favoring the plaintiff, and (4) advancement of the public interest
It's not clear that Sanofi could meet any one of these. The court at the outset would tend to defer to the FDA, which is in conflict with (1); Sanofi would not suffer irreparable damage (as monetary damages would suffice); the balance of hardship is equal or in Momenta's favor; and if they defer to the FDA judgment on safety/efficacy the public interest supports competition.