Credit Suisse's biggest backer, Saudi National Bank, has said it won't provide further financial help for the bank.

Speaking to CNBC's Hadley Gamble during a panel session in Riyadh, Saudi Arabia, on Wednesday morning, Credit Suisse Chairman Axel Lehmann declined to comment on whether his firm would need any sort of government assistance in the future.

Shares of Credit Suisse on Wednesday plunged to a fresh all-time low for the second consecutive day after a top investor in the embattled Swiss bank said it would not be able to provide any more cash due to regulatory restrictions.

Trading in the bank's plummeting stock was halted several times throughout the morning as it fell below 2 Swiss francs ($2.17) for the first time.