Defending champion Rory McIlroy was reportedly battling a back injury ahead of Thursday's opening round of the season-ending US PGA Tour Championship, where top-ranked Scottie Scheffler enjoyed a two-stroke lead.

The Golf Channel, citing unnamed sources, reported that the four-time major winner from Northern Ireland injured a muscle in his lower back while at home on Monday and had not practiced or played since.

McIlroy was considering withdrawing from the 30-player event, according to the report, but after treatment sessions Thursday and hitting 20 balls on the driving range, decided to play the opening round at East Lake in Atlanta.

The Tour Championship will award an $18 million playoff bonus prize to the winner based on season points.

It begins with a staggered score start based on season points, with Scheffler set to open later on 10-under, Norway's Viktor Hovland next on 8-under and McIlroy third on 7-under.

If he withdraws, McIlroy would finish 30th on the final points list for a $500,000 last-place payout.

Last year, McIlroy charged back in the final round to edge Scheffler for the title.

McIlroy, who won last month's Scottish Open for his 24th PGA Tour title, had used a new putter the past two weeks but was expected to go back to his more regular putter this week.

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