As the wrenching shifts within the American financial industry shook world markets on Wednesday, Morgan Stanley, one of the two major Wall Street banks left standing, was considering a possible merger with the Wachovia Corporation or another bank, according to people briefed on the discussions.

A tie-up with a bank would restore Morgan Stanley to its structure during the Depression, when the firm split from the Morgan banking empire. It would also leave Goldman Sachs, long the envy of Wall Street, as the only major American investment bank left.

As Morgan Stanley’s share price came under renewed assault on Wednesday, the firm’s chief executive, John J. Mack, received a telephone call from Wachovia expressing interest in the Wall Street bank. Other banks have also expressed interest in Morgan Stanley, which is considering various options. The talks with Wachovia are preliminary and no deal may emerge.