Jason Day withdrew from the Arnold Palmer Invitational on Thursday morning, citing back issues.
Day was two over through six holes at Bay Hill and had just hit his second shot at the par-5 16th into the water when he decided to pull out of the tournament.
Day is a former API winner, capturing the event in 2016. When he won his next event, the WGC-Match Play, it propelled Day to the No. 1 world ranking.
Though the 2015 PGA champ has not won since last May, his 2019 campaign was off to an auspicious start. He entered Orlando off back-to-back top-five finishes at Torrey Pines and Pebble Beach.
Day spoke to Golf Digest's Dave Shedloski in the locker room at Bay Hill as he was getting an adjustment from a chiropractor. He confirmed an earlier report that he was practicing last week at TPC Sawgrass—site of next week's Players Championship, an event Day won in 2016—but woke up Sunday and "couldn't really walk" because of back pain. An MRI revealed an injury to his L4-L5 discs.
"Just bending over I almost felt a little sick [from the pain]," said Day, who withdrew from the Wednesday pro-am at Bay Hill because of the back issue.
Asked about playing next week at the Players, Day said he wasn't sure his status, noting "I'm going to try."
This is Day's ninth career WD on the PGA Tour.