Rule Breakers analyst Karl Thiel told subscribers recently that he thought Momenta Pharmaceuticals (Nasdaq: MNTA) was likely undervalued, but that the company wouldn't reach full value until investors get over their "wall of worry."

After handing down a ruling yesterday that Momenta's generic version of sanofi-aventis' (NYSE: SNY) Lovenox could stay on the market, it seems that a judge pulled out a ladder and helped boost investors closer to the top of that wall. Sanofi had filed a lawsuit claiming that the Food and Drug Administration shouldn't have approved the generic version of the complex molecule.

It was a long shot by Sanofi, but the loss of generic Lovenox would have been a huge deal for Momenta, since that's its only product. Shares are up 4% today.

The wall of worry hasn't crumbled completely, though. Momenta's deal with marketing partner Novartis (NYSE: NVS) calls for Momenta to get 40% to 50% profit share if there is only one generic on the market. If the FDA approves another one, Momenta would take a triple hit: The market share for generic Lovenox would go down, the price would fall because of competition, and Momenta would only get a royalty in the high-single to low-double digit range. Investors will likely remain worried until the FDA makes a decision about a pending application from Teva Pharmaceuticals (Nasdaq: TEVA), and another from Amphastar Pharmaceuticals, which is partnered with Watson Pharmaceuticals (NYSE: WPI).

Trying to figure out what the FDA will do in this situation is nearly impossible. The agency took nearly five years to approve Momenta's drug, because the company had to convince the FDA that it could fully characterize the complex molecule that makes up Lovenox's active ingredient. Without a lot of inside knowledge, it's impossible to know whether Teva or Amphastar have the same capability to satisfy the FDA.

A quick rejection that sends potential competitors back to the drawing board would be the best thing for Momenta's stock. But at this point, time is working in favor of the company as well. The longer Momenta goes without additional generics being approved, the more money the company makes, and the more likely investors are to scale that wall of worry on their own.

To see the analysts' current thinking on Momenta, which was recommended back in 2006, grab a 30-day trial subscription to the Motley Fool's Rule Breakers newsletter. You'll get access to all our back issues and the most recent picks.