Mickelson did not elaborate on the reason in a statement released by Gaylord Sports.
``He's made a personal, private decision that he's not going to discuss,'' spokesman T.R. Reinman said.
Mickelson, who is No. 3 on the money list with nearly $5.7 million, did not play in 2001 because of the birth of his second child. He was not eligible for the Tour Championship two years ago.
He has a history of scaling back his schedule after the four majors, playing no more than five tournaments after the PGA Championship since 2001.
Even as early as February, Mickelson was vague about his schedule late in the year. Asked at the Match Play Championship if he had formulated a plan for post-majors events such as the Tour Championship, he said, ``I know what I'd like to do. But what I'd like to do and what I will do are different things.''
He mentioned that having a chance to win player of the year or the money title -- neither of which he has won -- are ``things that need to be considered.''
``But what happens for me personally is my kids start school at the end of August,'' Mickelson said at La Costa. ``It's a lot harder for them to travel, and I'd rather be home.''
He was specifically asked that day if he would play in the Tour Championship, but did not answer directly.
``It's late in the year,'' he replied. ``It's anticlimactic.''
Mickelson and Tiger Woods are among those who have argued that the season is too long.
PGA Tour commissioner Tim Finchem has been working on a new schedule for the 2007-10 television contract, in which the Tour Championship would be played in mid-September and preceded by three blockbuster tournaments.
Mickelson captured his second major this year at the PGA Championship, winning with a birdie on the last hole at Baltusrol. He now has 27 career victories, but only two of them -- the 2000 Tour Championship and the 1998 World Series of Golf at Firestone -- have come after the majors were over.
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