ORLANDO – Jason Day has surprisingly withdrawn from the first round of the Arnold Palmer Invitational after hitting his second shot on the 16th hole Thursday.

Playing with Rickie Fowler and Ian Poulter, Day hit his shot and then left the course on a golf cart. Golf Channel’s Will Gray reported Day suffered a back injury and an MRI this week revealed a tear in his L4-L5 discs.

Day practiced last week at TPC Sawgrass, home to The Players Championship, the PGA Tour’s flagship event which will be played next week. Day, who won the Players in 2016, said he aggravated his back Sunday and did not play practice rounds this week at Bay Hill.

“My back was sore when I was practicing from Tuesday to Saturday and I was going to practice on Sunday, but I woke up and couldn’t really walk or sit in the car,” Day told the Australian Associated Press after his WD. “I was on a dose pack to try to get the inflammation out of it and that didn’t get any better. I saw a physio here and tried to do as much work as I possibly could to get ready for this week.

“I couldn’t play at 100 percent today, so I just wanted to see if I could get out here and may have loosened up. But unfortunately it didn’t, so I had to pull out.”

Starting on the back nine in the first round at Bay Hill, Day was 2-over through six holes after a bogey on his opening hole, a double bogey on 13 followed by a birdie on 14.

Spoke to Jason Day after his WD. Said he practiced last week at Sawgrass but woke up Sunday and "couldn't really walk" because of back pain. MRI revealed annular tear in L4-L5 discs. Status for Players Champ TBD. — Will Gray (@WillGrayGC) March 7, 2019

Ranked No. 11 in the world, Day was T4 at the Pebble Beach Pro-Am in his last start. The Australian has 12 PGA Tour wins in his career, including the 2016 API.

Day, 31, has struggled with back injuries throughout his career. In 2016 he withdrew from the Tour Championship because of back pain, and at the time he was No. 1 in the world. He also withdrew from the BMW Championship during the FedExCup playoffs that year.

He said earlier this year that he had focused on his iron play in the off-season after winning twice on the PGA Tour in 2018.

“The way I finished the FedExCup championships, I didn’t finish well there, I finished 17th or 18th,” he said in January. “Even though I had won twice, I didn’t really compete where I really wanted to and that was in the big stuff.”