GWANGJU, South Korea -- Katie Ledecky withdrew from the 200-meter freestyle preliminaries and the 1,500-meter final Tuesday at the world swimming championships because of illness.
Her coach Greg Meehan said doctors were assessing Ledecky, but had no official diagnosis.
"She woke up this morning and she's not feeling well at all," he said. "I'm hopeful that we see her racing again this week."
The eight-day meet ends Sunday.
"This is brutal for her not to be competing," Meehan said, noting Ledecky's famous competitive nature.
Shortly after Meehan spoke to reporters, USA Swimming said Ledecky was out of the evening's 1,500 free final.
Ledecky was the fastest qualifier for the grueling event in 15 minutes, 48.90 seconds -- 2.68 seconds faster than the next-quickest swimmer. But the 14-time world champion hasn't been in the pool since Monday's prelims.
"If you get back into racing too early, it's just going to make the road to recovery a little bit longer," Meehan said. "We're just in a kind of half-day by half-day (mode) and hoping that she turns the corner here quickly."
U.S. national team managing director Lindsay Mintenko said Ledecky hasn't been feeling well since she arrived in Gwangju on July 17.
She was being seen by U.S. national team medical staff at the athletes' village. Meehan said doctors were awaiting lab results.
Ledecky had been scheduled to swim in Tuesday's morning heats of the 200 free, one of the showcase events in the pool.
It would have been a rematch between her and Australia's Ariarne Titmus, who stunned Ledecky to win the 400 freestyle final on Sunday. The event also includes Federica Pellegrini of Italy, Sarah Sjostrom of Sweden and Penny Oleksiak of Canada.
Also dropping out of the 200 free were Australia's Emma McKeon and Canada's Taylor Ruck.
McKeon was reported to not be feeling well, and Ruck instead wants to focus on her remaining events.
"The three girls that pulled out are probably my top three challenges, so it's a little bit easier now," Titmus said. "But Pellegrini's still in there, Sarah's still in there, so it's still a really tough challenge."
Sjostrom advanced to the semifinals with the fastest qualifying time of 1:55.14.
Meehan said Ledecky's illness was not an excuse for her second-place finish in the 400.
However, she had the slowest last lap of anyone in the final. Titmus went 1.83 seconds faster than Ledecky over the last 50 meters.
"There's having trouble finishing a race and then there's coming home in 31.7, and I think that was maybe a little bit of a sign," Meehan said. "She was really having a hard time through the last third of that 1,500 yesterday. I was worried about her at that time."
Ledecky's lone remaining individual event is the 800 free, and the preliminary heats are on Friday.
"We're heartbroken for her because she really had come in in a great position," Meehan said, "and hopefully we get to see that at some point this week."
On the men's side, there won't be another podium protest by Mack Horton in the 800-meter freestyle at the world swimming championships.
The Australian failed to qualify for the eight-man final. He finished 14th in Tuesday's preliminary heats with a time of 7 minutes, 52.65 seconds.
Horton's rival, Sun Yang of China, grabbed the last spot for the final on Wednesday. He was timed at 7:48.12.
Horton refused to step onto the podium or shake Sun's hand after finishing second to Sun in the 400 free on Sunday. The Aussie received a standing ovation from his fellow swimmers in the dining hall at the athletes' village that night.
FINA, swimming's world governing body, sent warning letters to Swimming Australia and Horton after the protest.
The Associated Press contributed to this report.