Reigning Masters champ Rory McIlroy withdraws from PGA event 1 month before green jacket defense

Rory McIlroy's green jacket defense appears to be a bit up in the air.

The reigning Masters winner was forced to withdraw from the Arnold Palmer Invitational on Saturday after suffering back spasms during his range session.

"While warming up in the gym this morning, I felt a small twinge in my back. As I started hitting balls on the range before the round, it worsened and developed into muscle spasms in my lower back," McIlroy said. 

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"Unfortunately...