Former world number one Luke Donald will contest next week's Open Championship after Jaco van Zyl withdrew from Royal Troon in order to prepare for the Olympics.
Van Zyl, who has also pulled out of the US PGA Championship at Baltusrol, only qualified for the South African team after Louis Oosthuizen, Charl Schwartzel and Branden Grace withdrew their names from consideration.
But the world number 65 hailed the Games as the "pinnacle of all sporting events" and cited fatigue from a busy season as the reason behind his decision.
"I was really starting to feel the effects of a very packed schedule at the French Open last week," Van Zyl told South African Golf Association media liaison, Lali Stander.
"I have been at it almost non-stop since I returned to golf last January. I've had a jam-packed season this year, including a lot of travelling between continents, and then coming home to the added stress of building a house.
"This was definitely wasn't a decision I took lightly, but something had to give and I decided to forego the majors in July in favour of the Olympics.
"I expect that there will be a camp that will criticise me for withdrawing from the majors, but I feel very passionate about golf's debut at the Olympics. Rory (McIlroy) said in a recent press conference that we play four "Olympics" a year because major titles are what we play for, but I don't agree.
"To me, the Olympics is the pinnacle of all sporting events and to have the chance to represent Team South Africa on sports' biggest stage is an honour I don't take for granted.
"I need to go to Brazil with the rest of the South African team knowing that I am in peak mental and physical health and that I can give my best over four rounds. The majors will still be there next year, but I don't know if I will get another chance in 2020."
Donald missed the cut in his first five Open appearances, including the last time the Open was staged at Troon in 2004, but was 12th at St Andrews last year.
Former champion Stewart Cink, who defeated Tom Watson in a play-off at Turnberry in 2009, also withdrew on Wednesday to allow fellow American Daniel Summerhays into the field.
No reason was given for Cink's withdrawal, although the 43-year-old took a break from the game earlier this season after his wife Lisa was diagnosed with breast cancer.
On May 26, Cink wrote on Twitter: "Future schedule uncertain, likely to be sporadic. Mainly plan to be there for @lisacink. Will throw in some events when she's feeling well."
Americans Jamie Lovemark and Colt Knost are now first and second reserve.
Press Association Sport