Michael Rogers' heart problem has forced the Australian cycling star to pull out of the Dubai Tour.
The 36-year-old went on Twitter to explain why he did not start Friday's third stage.
Sport: The week's best plays
From offloads to Open glory, these are the most exciting, silly and downright crazy plays in the sporting world this week.
"No start for me this morning at Dubai Tour. My heart data from stage 2 shows Im not yet ready to compete at such a high level. #stepbystep," Rogers posted.
The three-time world time trial champion was forced to postpone his start to the season when routine tests late last year caused concern.
Rogers was diagnosed in 2001 with a congenital bicuspid aortic valve.
The tests in December showed the condition had progressed, forcing Rogers to sit out last month's Australian road nationals and the Tour Down Under.
Specialists then gave Rogers the green light to return to racing at the Dubai Tour and he said this season would be his last.
He wants one more Tour de France in the Tinkoff-Saxo team as a key climbing domestique for Spanish star Alberto Contador.
But before the Dubai Tour, Rogers admitted he would have to see how his heart coped with racing intensity.
"Ultimately there might be a decision to make, but we'll take it one step at a time," he told the cyclingnews website.
No start for me this morning at Dubai Tour. My heart data from stage 2 shows I’m not yet ready to compete at such a high level. #stepbystep.— Michael Rogers (@mickrogers) February 5, 2016