New York - Tiger Woods struggled with a stiff back on Wednesday, limited to chipping and putting on the back nine of his pro-am round on the eve of the PGA Tour's playoff opener.

World No 5 Woods tees off in Thursday's opening round of the Northern Trust, the first of three tour playoff events culminating with the Tour Championship, where Woods is the defending champion.

Woods, the reigning Masters champion, has played a limited schedule this season in hopes of keeping himself healthy at age 43, but admits he has days when he faces major back issues and others when he can drive the ball with golf's best.

"This is how it is. Some days I'm stiffer than others," Woods said.

"I was out there hitting it great. Driving it out there with Brooksy and DJ (long-hitters Brooks Koepka and Dustin Johnson).

"Today I'm stiff. Hopefully I'm not that way tomorrow."

Woods, a 15-time major champion chasing the all-time record 18 majors won by Jack Nicklaus, has 81 career PGA titles, one shy of matching Sam Snead's all-time record.

Woods tees off alongside fellow Americans J.T. Poston and Scott Piercy on Thursday morning at Liberty National in Jersey City, New Jersey.

At 28th in the season points standings, just behind his playing partners for the first two days, Woods is in danger of failing to qualify for a chance to defend his Tour Championship crown.

He must be in the top 30 after next week at Medinah to reach the season finale at Atlanta's East Lake. Playing all three would be his longest run of events since last year's playoffs, when he was testing his recovery from a spinal fusion.

"I learned a lot last year by playing too much," Woods said.

"Coming back from my procedure and not really knowing what to expect, I pushed it pretty hard. I vowed I would never do that again.

"Now we have a more condensed season and it's trying to figure out how to stay sharp, practice and also have my back feeling good all the time. It's a challenge."

Woods hasn't played back-to-back weeks since February.

"There's concern, hopefully because of the pressures I'm going to be facing," Woods said. 

"I'm trying to get myself where I'm in contention, where it takes a toll on you."

Woods won for the first time since 2013 last year at East Lake, then captured his first major title since the 2008 US Open at the Masters in April at Augusta National.

Since capturing a fifth green jacket, Woods has played only four times - missing the cut at the Open Championship and PGA Championship, sharing 21st at the US Open and ninth at the Nicklaus-hosted Memorial, a US Open tune-up.

Woods was twice a runner-up at the Northern Trust at Liberty National, in 2009 and 2013. The latter loss, to Adam Scott by a stroke, was one of the first places where Woods was severely nagged by back spasms.

Woods was at Liberty National in 2017 as a Presidents Cup assistant captain to Steve Stricker. This year, Woods will captain the American squad that will travel to Australia to defend the trophy at Royal Melbourne.

Woods ranks 12th in the standings for making the Presidents Cup team with two events remaining but says his being there as a player is not assured.

"The top eight after next week. That's what's guaranteed," Woods said.

Woods will make four captain's picks to complete the US line-up, his decision not coming until the WGC HSBC Champions.

But for now, Woods is trying to become the first player to win the PGA playoff title three times in his career.

"He's Tiger Woods. He doesn't need to prove anything to anyone," said four-time major winner Rory McIlroy.

"He doesn't need to prove anything else to himself. He can put the clubs away tomorrow and live happily ever after.

"But he wants to compete. He's a competitor. I think it shows a lot that he still turns up to some events and wants to play."