Luke Donald has withdrawn from his final event of the year after seeking medical advice for chest pains he experienced in Sea Island, Georgia.
The 39-year-old former world number one was originally in the field at the RSM Classic but, as pain in his chest grew worse across Thursday, he forfeited and sought treatment at a local hospital.
England's Donald posted on his official Instagram page: "Well that wasn't quite the finish to my year I had in mind!! Had some chest pain last night and into this morning & it kept getting worse.
"After some medical advice, I had to withdraw & was shipped off to the hospital to get my heart looked at. After 7 hours of tests all looks good with my heart thankfully.
"A big thank you to the staff at the South East Georgia Brunswick hospital for taking good care of me.
"Time to put my feet up for a few weeks, recharge, regroup and get ready for a big 2018."
Donald, whose last win on the PGA Tour came in 2012, had been partnered with Brandt Snedeker and Sea Island resident Matt Kuchar for the first two rounds.
Chris Kirk carded an eagle on the final hole to secure his spot at the top of the leaderboard.
The event, which is played on two courses, saw players take on either the Plantation Course or the Seaside Course, with the seven lowest scores of the first day coming from the former.
Kirk walked in his eagle putt from 17 feet on the par-5 18th hole, finishing the round with a nine-under 63 and putting him one shot ahead of his closest rival Joel Dahmen.
There was a three-way tie for third place, with Jason Kokrak, Hudson Swafford and Brian Gay all scoring seven-under 65.
University of Georgia alumnus Swafford, one of 12 local residents playing in the tournament, sank a 27-foot putt for birdie on the par-5 8th hole.
Scotsman Russell Knox carded an opening-round five-under 67, putting him in eighth place alongside nine others, with six birdies and a bogey on the par-3 15th hole.
Meanwhile, former FedEx Cup champion Brandt Snedeker made his first appearance since June, despite still suffering from a chest injury which has marred his season.
Playing on the the Seaside Course, he finished at three-under 67 and later told the PGA Tour website he was hoping to "get back in the mix" with a low round on day two.
Kirk is aiming to clinch his fifth PGA Tour victory, having won at Sea Island four years ago.