Australian Olympic champion Kyle Chalmers on Wednesday pulled out of July's world titles in Budapest to have surgery for a worsening heart condition.
The Rio 100m gold medallist suffers from supraventricular tachycardia (SVT), which occasionally causes his heart to race but is not normally life threatening.
It forced the teenager to miss Australia's national short course championships late last year, and his doctor and coach have now decided he needs surgery sooner rather than later to help prolong his career.
"The symptoms have reached a point where I must act to ensure I am in peak physical condition for next year’s Commonwealth Games trials and hopefully the Commonwealth Games,” said the 18-year-old of the event on home soil at the Gold Coast.
"There is never a good time for this type of procedure but given I’ve suffered from these symptoms during two of the past three major meets, and following my doctors advice, I have made the tough decision to withdraw (from Budapest).”
National head coach Jacco Verhaeren said Chalmers' health was of paramount importance.
"Kyle has our full support and we know he will use this time away from competition positively and to his advantage to return for a home Commonwealth Games in 2018 and beyond,” he said.
He is due to have surgery in the coming weeks.