Edison - PGA Championship winner Jason Day pulled out of Wednesday's pro-am at the Barclays with a bad back, hoping the rest would have him fit to tee off Thursday in the first event of the PGA Tour playoffs.
Day's physiotherapist and trainer Cornel Driessen told PGATour.com that the Australian "tweaked" his back moving an item under his motor coach on Tuesday night.
"This is a precautionary withdrawal for a long-standing disc issue," Driessen said.
Day captured his first major title at Whistling Straits on August 16, beating Jordan Spieth by three strokes to lift the PGA Championship trophy.
He is scheduled to tee off on Thursday in the $8.25m Barclays alongside Masters and US Open champion Spieth and two-time Masters winner Bubba Watson.
Dustin Johnson also pulled out of Wednesday's pro-am, complaining of chest congestion.
He, too, was hoping to tee off on Thursday when he is scheduled to play with fellow American Patrick Reed and New Zealand's Danny Lee.