The recent decline in Citigoup stock is "difficult to watch and naturally reminds all of us of what happened several years ago [but] there is little similarity between now and then," Vikram Pandit said in a voicemail to Citi employees on Tuesday, The WSJ reports.

Bank of America CEO Brian Moynihan similarly sought to allay his employees' concerns, declaring in a company-wide memo: "The most important point to remember is that our company remains financially strong." (Moynihan, who was also on CNBC yesterday, is participating in a unique public conference call later today, hosted by one of its biggest shareholders Fairholme Capital Management.)

Translation: Remain calm, all is well. Nothing to see here folks. Keep moving.

But big bank CEOs, and their defenders, doth protest too much, according to Columbia Professor and two-time Nobel Prize winner Joseph Stiglitz.

There is "considerable" risk in the banking sector today, Stiglitz tells Jeff Macke and me in the accompanying video. In addition to a slowing economy, today's problems are largely the result of regulators' failures to tackle the problems that both caused and were revealed by the 2008 crisis: Excessive leverage, lack of transparency and distortions created by 'too big to fail' institutions.

The 'too big to fail' problem has only gotten worse since 2008 — the biggest banks control an even greater portion of U.S. deposits -- and Stiglitz is particularly concerned nothing has been done to make bank holdings more transparent.

"We don't know the kinds of exposures to say European [credit default swaps] American banks have," he says. There are rumors that as much as 50% of European sovereign bonds are insured thru CDS by American banks, he notes. "But we don't really know."

As was the case in 2008, the lack of knowledge of what's on bank balance sheets poses the risk of banks refusing to lend to other banks, Stiglitz says. "If one of these countries has a real difficulty [interbank lending] markets will freeze up."

Forget laughter. Does anyone remember "counterparty risk? This is what I was referring to Monday when I said the similarities between now and 2008 outweigh the differences. (See: 2008 Redo? History Doesn't Repeat, But It Often Rhymes )

Stiglitz addressed these and related issues in testimony before the Senate Banking Committee last week: "It is precisely because the economy is fragile, banks have inadequate capital, and the banking sector in the aftermath of the crisis is more concentrated than before that the risk of a financial catastrophe of the kind that we experienced in 2008 is so great today," he said. "The downside risks of not doing something are especially grave now.

Notably, those comments were made on Aug. 3, prior to the most acute moments of the recent sell-off, which resumed in earnest Wednesday morning.

The latest decline comes amid concerns about Europe and the potential contagion emanating from its sovereign debt crisis which, in turn, is putting renewed pressure on shares of big European banks like Societe Generale, BNP and Deutsche Bank, as well as their U.S. counterparts including, but not limited to, Bank of America and Citigroup.

See also: Failed Monetary Policy Helped Create the Economic Crisis, Stiglitz Says

Aaron Task is the host of The Daily Ticker. You can follow him on Twitter at @atask or email him at altask@yahoo.com