Credit Suisse Chief Executive Officer Tidjane Thiam on Monday said that it's "hard to understand" why investors are suing the bank over a complex financial product that yielded steep losses for some.

Known as the VelocityShares Daily Inverse VIX Short-Term Exchange-Traded Note (ETN), the instrument is designed to go up when stock market volatility goes down. Last month, it sank by more than 90 percent in just hours in the wake of a market selloff.

In two lawsuits filed last week, investors sued Credit Suisse as well as its service provider Janus Index & Calculation Services — a unit of asset manager Janus Henderson.

On Feb. 5, the XIV plunged from $72.59 at 4 p.m. to $4.22 by 5:10 p.m., according to calculations from Reuters. One lawsuit claims that estimates of the XIV's value were not updated every 15 seconds, as would be typical.

Speaking to CNBC, Thiam said it was Janus, not Credit Suisse, that provided estimates of the notes' value. He also pointed to financial services firm S&P, which he said published the price.

The product has an inverse relationship to the VIX, which measures volatility in the S&P 500. , sometimes called the fear index, is also maintained and published by S&P Dow Jones Indices.

"(That) people will sue us for something we're not in charge of, it's hard to understand," Thiam said.

Investors said lofty estimates led them to buy the notes at inflated prices. According to the most recent lawsuit filed in the U.S. District Court in Manhattan, Credit Suisse did not announce the market disruption and Janus misreported the notes' value.

Janus Henderson and S&P Global did not immediately respond to CNBC's request for comment. Janus Henderson has previously denied any wrongdoing.

When asked if he thought that regulators should step in to monitor the issuance of such ETNs to retail investors, Thiam said that was a question for them.

"As a company we've been hyper clear … what the risks are. Really it's a matter for regulators whether they need to stop retail investors from investing in those."

— Reuters contributed reporting for this article.