Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of investment bank Jefferies Group (NYSE: JEF) were getting hammered today, falling as much as 14% in intraday trading on concerns over Greece's call for a referendum vote.

So what: Interestingly, Jefferies felt the need to issue a press release today saying that it has "no meaningful exposure" to debt from Portugal, Italy, Ireland, Greece, or Spain. That is no doubt a major issue on bank investors' minds today in the wake of Greece's call for a referendum vote on the recent bailout agreement as well as the failure of MF Global (NYSE: MF).

Obviously, the press release wasn't enough to keep Jefferies stock from tanking today. While some investors may have been encouraged by it, the downward pressure that Greece's move is putting on the entire banking sector makes it like trying to swim against a tsunami surge.

Now what: If Greece manages to succeed in unraveling its bailout and, possibly, its membership in the euro, that would be bad news for banks around the world -- whether directly exposed to European debt or not. Is Jefferies the bank I'd be most worried about, though? Hardly.

Want to keep up to date on these stocks?

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.