Jobs' latest medical leave, the third time since 2004, comes at a time when the world's most valuable technology firm faces the biggest threat from Google (GOOG.O), through its Android mobile operating system, which has seen torrid growth as the preferred choice of both iPhone and iPad rivals.
Samsung, at the forefront of the long queue of rivals determined to halt Apple's runaway boom in smartphones and tablets, is seen as a key threat, and its shares jumped more than 3 percent to a record, partly helped by such expectations.
"There'll be no fundamental change in Apple but the news of Jobs taking leave could sentimentally hit Apple shares and offer investors an opportunity to take profits from its shares, which have risen so much recently," said Lee Seung-woo, an analyst at Shinyoung Securities.
"Then Samsung is the best alternative for investors seeking exposure to the tech sector as it's the most formidable threat to Apple for now."
Apple's surprise announcement -- made on a U.S. market holiday -- dragged its shares down more than 6 percent down in European trading on Monday. They are up 62 percent in the past 12 months on the Nasdaq stock exchange.