(CNN) — Shares of Credit Suisse plunged more than 20% after its largest shareholder rejected more funding for the Swiss lender.

In an interview with Bloomberg, the head of the Saudi National Bank said it would not increase its stake in the Swiss lender.

“For many reasons, the answer is absolutely no. I cite the simple reason of regulatory and legal. Now we have 9.8% in the bank; if we go above 10%, all kinds of new rules will come into play. Either through our regulator or the European regulator or the Swiss regulator,” Ammar said. “We are not ready to enter a new regulatory regime,” Al Guthari told Bloomberg.

Al Qudayri made similar comments to Reuters at a conference in Saudi Arabia. He said he was happy with the turnaround plan and that the Swiss lender did not need any additional money.

“We are happy with the plan they have presented, the turnaround plan. It is a very strong bank,” Al Guthari told Reuters in an interview.

“I don’t think they need more money; if you look at their proportions, they are doing well. And they operate under a strong regulatory regime in Switzerland and other countries,” Al Qudayri said on the sidelines of a conference in Riyadh.

Shares traded down nearly 22% in Zurich on Wednesday.

Credit Suisse declined to comment.