Steve Jobs on a 'down cycle' recently, at Apple offices less frequently

Citing an anonymous source, The New York Times on Monday reported that Jobs, of late, would lunch in his office rather than where he typically would, in the company cafeteria. He also began a "down cycle" in recent weeks, and only came into the office about two days per week.

"Mr. Jobs suffers from immune system issues common with people who have received liver transplants and, as a result, his health suffers from frequent 'ups and downs,' according to a person with knowledge of the situation, who agreed to speak on condition of anonymity because he was not authorized to discuss it," author Miguel Helft wrote.

Earlier Monday, Jobs announced in a letter to employees that he would take a medical leave of absence so he can focus on his health. He will remain CEO and will be involved in "major strategic decisions" for Apple.

Jobs declined to reveal exactly what his medical condition may be. He noted that he and his family would "deeply appreciate respect" for their privacy. The Apple co-founder has long said he believes his health is a private matter.

Jobs returned to work in June 2009 after a liver transplant. In subsequent interviews he was upbeat and said he felt healthy, but the report from the Times would indicate that the CEO has fallen on hard times in recent weeks.