The former No. 1 golfer said the last few months have been more challenging than his return from previous injuries.
"There is no comparison between a knee and a back," he told reporters. "This thing is just way different. It's way more debilitating than I thought."
The WGC-Bridgestone tees off on Thursday at Firestone Country Club in Ohio. As the defending champion, Woods is hoping for a better showing than he managed at the Quicken Loans National and the British Open.
"Everything needs to get a little bit better," he said. "My good shots are still really good. My bad shots need to be in positions where I know I should miss the golf ball."
Gradually increasing his practice time, Woods has tried to remain patient about regaining top form, saying: "It takes a little bit of time."
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