Apple shares were down 3% on the news as Apple sites buzzed with speculation that Jobs decision not to address one of the highlights of the Mac calendar was related to his health and possibly that Apple was behind on product delivery.
The lack of the Apple CEO's presence at the IDG-owned show marks the first time in a long time that he will not have appeared.
In 2004 he underwent surgery to remove a rare type of pancreatic cancer.
Reuters quoted analysts that said Apple's withdrawal from Macworld did not necessarily mean that Jobs was sick, but could indicate that the company has no blockbuster product announcements.
Apple spokesman Steve Dowling told Reuters: "Phil is giving the keynote because this will be Apple's last year at the show, and it doesn't make sense for us to make a major investment in a trade show we'll no longer be attending."
Apple went further in its press announcement and also said that 2008 would be the last year it will exhibit at Macworld Expo.
Instead of Jobs, Philip Schiller, Apple's senior vice president of worldwide product marketing, will deliver the keynote speech next month in San Francisco.
It said it was ending its association with Mac Expo explaining, "trade shows have become a very minor part of how Apple reaches its customers". Instead it claims the increasing popularity of Apple's Retail Stores and the Apple.com website allows it to directly reach more customers.
Apple has been steadily scaling back on trade shows in recent years, including NAB, Macworld New York, Macworld Tokyo and Apple Expo in Paris.
Apple shares, which have almost halved since June like many technology companies, have also been hit over fears about a drop-off in consumer spending.
In July Apple shares fell down 10% after the iPod manufacturer projected a drop in sales and profit growth for the last quarter of its fiscal year.
Its shares then were trading at around $150 and are now trading at $95.43.