Jason Day has withdrawn from Ernie Els' International Presidents Cup team for their clash against the United States next month, and he has been replaced by South Korea's Byeong Hun An.
Day, 32, announced on Friday that his troublesome back injury had once again been causing him difficulties and he has therefore chosen to step down from the biennial contest.
The Australian had been one of Els' four captain's picks after failing to qualify automatically for the side following an indifferent season that was plagued more often than not by his back injury.
"Frustratingly, I've been through back problems before and my medical team decided it best to shut down all practice and play," said Day in a statement.
"Therefore I wanted to inform Golf Australia as well as provide Ernie as much time as possible to best prepare our International Team for Royal Melbourne.
"I look forward to playing at home in the near future. My best to all the competitors in Sydney and my teammates in Melbourne."
Despite once reaching World No.1 status, the 12-time PGA Tour winner has fallen rapidly down the rankings to a current 31st.
His last victory on the PGA Tour came in May 2018 at the Wells Fargo Championship.
Els has chosen to replace Day with former BMW PGA champion An, who will make his Presidents Cup debut.
An, 28, has yet to win on the PGA Tour but appears to be finding his form right now with four top-15 finishes in his last six starts, including a third at the Sanderson Farms Championship.
In August 2009, An became the youngest ever winner of the US Amateur.
Day's absense will likely give the United States even more of an advantage than they already had on paper, but captain Els is not treating it that way.
"We wish Jason well and hope his back recovers quickly," said Els.
"The good news is that there were a number of strong and qualified players available to choose from when I made my captain's selections.
"To have someone as steady and talented as Ben puts us in a great position to succeed."
The United States have won 10 of the 12 Presidents Cup matches, with the Internationals winning just once at this year's venue, Royal Melbourne, back in 1998 by a scoreline of 20.5-11.5.
This year's contest will take place from December 12 to 15.