By Mark Lamport-Stokes (Reuters) - Tiger Woods' decision to rule himself out of contention for next month's Ryder Cup was a wise one given his struggles since undergoing back surgery in March, but it also raises fresh concerns over the former world number one's playing future. Though he says he has always recovered quickly from surgeries, he looked tournament rusty and a shadow of his former self in his last four PGA Tour appearances, twice missing the cut and once withdrawing midway through the final round. The 14-times major winner has had four knee surgeries over the years, along with a string of other injuries, and undergone several swing changes in an attempt to limit the more severe effects of the golf swing on his body. Yet former PGA Championship winner Paul Azinger believes Woods' problems this year are not purely physical, and that perhaps he has spent too much time on yet another overhaul of his swing. More...