NEW YORK—Apple Inc.’s shares fell as much as 6.5% Tuesday, erasing up to $20 billion in market value, after the consumer-electronics maker disclosed that Chief Executive Steve Jobswould take another unexpected medical leave.

The decline, however, is more moderate than its retreat on Monday during overseas trading—the U.S. market was closed for a holiday—suggesting that investors are focusing instead on the company’s upcoming quarterly earnings report and growth prospects.

“While this creates uncertainty, we believe the product pipeline is set for the next two years and Apple’s bench strength has come through before,” said Peter Misek, an analyst for Jefferies & Co.

After the initial sharp decline Tuesday, Apple shares rebounded, recently falling 3.7% to $335.63. Based on that price, the stock remains up 4% this month from its 2010 close of 322.56 and the company carries a market cap of about $308 billion, keeping Apple as the world’s most valuable technology company.

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