Credit Suisse shares nosedived to historic lows on Wednesday after its main shareholder said it would not invest any more money, as market jitters over European lenders spiralled in on the Swiss bank.
Switzerland's second-biggest bank, hit by a series of scandals in recent years, saw its share price tumble off a cliff after Saudi National Bank chairman Ammar Al Khudairy said it would "absolutely not" up its stake.
His comments came as European stock markets plunged amid renewed concerns about the banking sector.
In London, the FTSE 100 finished 3.8 percent lower at 7,344.45, the DAX in Frankfurt ended down 3.3 percent at 14,735, and the CAC 40 in Paris fell 3.6 percent to 6,885.
Credit Suisse's market value had already taken a heavy blow this week over fears of contagion from the collapse of two US banks and its annual report citing "material weaknesses" in internal controls.
The bank's shares were quickly in free fall on the Swiss stock exchange, plunging more than 30 percent to a record low of 1.55 Swiss francs.
The bank regained some ground by the close, ending the day's trading 24.24 percent down at 1.697 Swiss francs.
Fears about the bank were spreading beyond Switzerland's borders.
A US Treasury spokesperson said the finance ministry was "monitoring" the problems surrounding Credit Suisse and was "in touch with global counterparts".
And French Prime Minister Elisabeth Borne called on the Swiss authorities to step in and "settle" the problem, adding that the French and Swiss finance ministers were due to speak in the next few hours.
Amid the market panic, Credit Suisse chairman Axel Lehmann insisted at the Financial Sector Conference in Saudi Arabia that the bank did not need government assistance, saying it "isn't a topic".
"We have strong capital ratios, a strong balance sheet," Lehmann said, adding: "We already took the medicine," referring to the bank's drastic restructuring plan revealed in October.
Credit Suisse is one of 30 banks globally deemed too big to fail, forcing it to set aside more cash to weather a crisis.
The bank and financial authorities remained quiet about the share fall.
But citing three anonymous sources, the Financial Times newspaper reported that Credit Suisse had appealed to Switzerland's central bank and its financial regulator for "a show of support".
Analysts warned of mounting concerns over the bank's viability and the impact on the larger banking sector, as shares of other lenders sank on Wednesday after a rebound the day before.
"Where one big shareholder goes, others may follow. Credit Suisse now has to come with a concrete plan to stop outflows, and do it fast," IG analyst Chris Beauchamp told AFP.
Neil Wilson, chief market analyst at trading firm Finalto, agreed.
"If Credit Suisse were to run into serious existential trouble, we are in a whole other world of pain. It really is too big to fail." (AFP)