The Queenslander withdrew from the BMW Championship with the same injury less than two weeks ago and was later diagnosed with an annulus ligament tear in a disc in his back.

After opening this tournament with a three under 67, Day said he was “cautiously optimistic” about being able to finish the tournament despite the shooting pain through his lower back.

Eight holes into his second round he was done.

Coming off a bogey-birdie-par run at the 5th, 6th and 7th holes, Day found water off the tee at the 8th hole. He tried to hit a driver off the deck and found trees. When he failed to reach the green with his next shot he picked the ball up and started walking to the clubhouse.

“Just not enough time to get it rested," Day told PGATour.com as he walked to the carpark.

"Jason has a strained ligament in his lower right back with muscle spasm." statement from Bud Martin, Jason Day's manager.

Day will now go into a seven-week period of rest and recuperation. His next tournament is the Emirates Australian Open at Royal Sydney, and he will tee up the following week with Adam Scott in the World Cup of Golf.

There will be undoubtedly some concern from Open and World Cup organisers that Day’s injury might prevent him from playing in their events. In 2014, Day withdrew from playing two Australia tournaments because of back spasms, which he said would react badly on the long flight home from the United States.

Day’s manager, Bud Martin, said in a statement that the 28-year-old would be fine with some rest in the offseason.

"Jason has a strained ligament in his lower right back with muscle spasm," the statement read.

"He withdrew as a precautionary measure. Jason should be fine with some rest after a long break in the offseason."

By Day withdrawing, US Open Champion Dustin Johnson has won the points-based PGA Player of the Year award and is likely to win the player vote as PGA Tour Player of the Year due to his three victories … with a fourth now becoming increasingly likely.

Dustin Johnson holds the halfway lead at East Lake by one stroke. PHOTO: Kev C. Cox/Getty Images.

Johnson added a three under 67 to his opening score of 66 to move to seven under and is one stroke ahead of fellow American Kevin Chappell at the halfway mark.

Johnson made back-to-back birdies on the 5th and 6th holes, before adding two more at the 10th and 11th. He gave a shot back at the par-4 12th when he failed to get up and down from a greenside bunker. A birdie-bogey-par finish saw him sign for 67.

East Lake is playing tough, tougher than most PGA Tour courses, and just ten players out of the elite field of 30 now remain under par.

One player sitting just outside red numbers is Adam Scott. His one over 71 could have been much higher if not for a bogey-free back nine of 32. In contrast, his outward half was disastrous. Three bogies and a double bogey at the tough par-4 8th hole, were only offset by the sole birdie at the 5th hole.

Although the 36-year-old lies at even par and just seven shots behind leader Johnson, it is going to take an incredible weekend of golf from Scott to overcome the American and win this title, which would also give him the FedEx Cup title and the $10 million bonus.

Against any other player this scenario might be plausible, but Johnson is the form player in world golf and his three victories already this year suggest he has become a feared front runner.