"To have someone as steady and talented as Ben An puts us in a great position to succeed", Els said. This start included top-10s at the Sanderson Farms Championship (3rd), The CJ Cup @ Nine Bridges (T6) and ZOZO Championship (T8).
Day recently confirmed he'd hired a "golf trainer" and a "physio trainer" to his team to help maintain his health after a series of predominantly back ailments in the past couple of seasons. He also finished T14 at the World Golf Championships-HSBC Champions and sits 16th in the FedExCup after the fall series.
"It was a huge surprise to receive a call from Ernie who told me that I was in the team", said An, the son of two Olympic table tennis medallists.
"It has been a goal of mine all season to be on the International Team and I am honored to play in my first Presidents Cup". Day has played in four Presidents Cups. Coincidentally current team members Marc Leishman, Louis Oosthuizen and Hideki Matsuyama were three of those debutants in OH and might be able to impart some wisdom to their teammates.
An gives the worldwide team a record-tying seven rookies as it tries to beat the USA for the first time since 1998. "If that's off the back of the rookies, so be it", Els said earlier this month.
Day, a former No. 1-ranked player in the world who won the 2015 PGA Championship, had been selected by Els as one of his at-large picks after a disappointing season that has seen him drop to No. 31 in the world.
Captain Ernie Els on Friday replaced Day with Ben An from South Korea. Day had been practicing in the Palm Springs, California, area to get ready for both tournaments.
"Frustratingly, I've been through back problems before and my medical team decided it best to shut down all practice and play".
"I look forward to playing at home in the near future".
An, who is best known for being the youngest victor of the US Amateur at just 17 as well as winning at Wentworth in 2015, is 43rd on the world rankings and he will arrive at Royal Melbourne with some decent form behind him in the past few months.
Day did not elaborate on his recovery period but it is likely he won't return before the Farmers Insurance Open on January 23-26 where he is a two-time champion.