Tiger Woods announced Tuesday he will not be able defend his title at this week's Arnold Palmer Invitational because of back spasms and said it was too early to know if he'd be ready for the Masters next month. Woods withdrew during the final round of the Honda Classic three weeks ago due to the issue in his back and was scheduled to return to action Thursday at Bay Hill at a tournament he has won eight times. But the reigning PGA Tour Player of the Year said on his website the spasms and pain in his back haven't subsided. Woods has made just four starts worldwide during this current season and has not finished better than a tie for 25th place at the WGC-Cadillac Championship two weeks ago. He failed to make the secondary cut at the Farmers Insurance Open and tied for 41st at the Dubai Desert Classic, a European Tour event, before withdrawing from the Honda Classic. Woods captured his second straight Bay Hill title last year, becoming only the second player to win the same event eight times after Sam Snead, who won eight Greater Greensboro Open titles.