"This squarely puts the pressure on Jerry Yang to deliver results and shareholder value," Standard & Poor's equity analyst Scott Kessler said. "You are going to see a lot of shareholders just throwing in the towel because they are going to realize it's going to take awhile for the stock to get back to where it was Friday."

　　Ballmer also will be under the gun to prove he can come up with another way to challenge Google Inc.'s dominance of the Internet's lucrative search and advertising markets.

　　The unsolicited bid was widely seen as Ballmer's admission that Microsoft needed Yahoo's help to upgrade its unprofitable Internet division.