Apple has announced that chief executive Steve Jobs will not be making the keynote address at the Macworld Expo in San Francisco next month.

The company also said that from 2010 it will no longer participate in the conference, which has become the prime convention for Macintosh developers.

For the event in January, Apple will send Phil Schiller, senior vice president of product marketing, who has often accompanied Jobs onstage in keynote speeches and product announcements.

The keynote will be the first at the San Francisco Macworld Expo not to be delivered by Jobs since he returned to the chief executive position in 1997. The annual conference is hosted by publishing firm IDG.

The news comes amid growing speculation that Jobs's health is in decline. Rumours have circulated in recent months that the Apple chief was suffering from complications in the aftermath of a battle with pancreatic cancer.

Apple claimed that Jobs's health had nothing to do with the move, saying in a statement that the decision was part of a larger overall strategy to reduce its presence at trade shows.

"Apple is reaching more people in more ways than ever before so, like many companies, trade shows have become a very minor part of how Apple reaches its customers," read the statement.

"The increasing popularity of Apple's retail stores, which more than 3.5 million people visit every week, and the Apple.com website enable Apple to directly reach more than a hundred million customers around the world in innovative new ways."

The Macworld Expo runs from 5 to 9 January at San Francisco's Moscone Convention Center.

The Co nsumer Electronics Show runs from 8 to 11 January in Las Vegas.