plummeted on the Swiss exchange amid talk Martin Ebner, the insurer's biggest shareholder, won't accept CS's offer for Winterthur announced on Monday.

Shares of Winterthur -- which has had a presence in Parliament Street, Bermuda, since 1994 -- fell 6.6 percent to 1,405 francs, while Credit Suisse dropped 6.5 percent to 190.25 francs. That contributed to the benchmark Swiss Market Index's 2.2 percent decline.

That's amid speculation Ebner's investment funds will reject the bank's offer of 7.3 Credit Suisse shares for every Winterthur share, traders said. Ebner spokesman Kurt Schildknecht said no decision had yet been made, and that it won't be announced before an extraordinary shareholders meeting slated for September 5, when Winterthur's investors will decide whether to accept the offer. "It's a fair price, but it's not an extremely good one,'' Schildknecht told Bloomberg News.

Since CS's bid was made public, the bank's shares have fallen 8.7 percent, lowering the value of its bid by almost 1 billion francs, 12.35 billion Swiss francs ($8.12 billion).

Ebner said last week he and his clients hold "about 30 percent'' of Winterthur shares, making him the insurer's biggest shareholder. Others include Swiss Reinsurance Co., which owns about 5 percent of the bank's shares. When the offer is completed, Ebner's funds will own 6 to 7 percent of Credit Suisse, Schildknecht said. That would make them Credit Suisse's second-largest shareholder after bank employees, according to CS Group.