Kristof Milak, who won two golds at the 2022 world swimming championships, said on Wednesday he will skip this year's event in Japan claiming: "I am currently neither physically nor mentally in a position to be among the best in the world."
The 23-year-old Hungarian won two butterfly golds last year before home fans. He is also the world record holder and Olympic champion in 200m butterfly and won the 2019 world title in the event.
"It is with a very heavy heart that I have made a decision," he said in a statement posted by his club, Honved, on Facebook. "I will not compete in the World Championships in Fukuoka in July - as much as I would like to continue my winning streak."
Milak said that he was trying to understand a dip in his form.
"I am looking for the satisfactory answer myself as to why it happened this way," he said in a statement posted by his swimming club, Honved, on Facebook.
"I could not even approach one hundred per cent of my performance, which is essential for peak performance, and I don't like to settle for less."
The Budapest showpiece was the first of three world championships in 19 months with Fukuoka in July followed by Doha in February 2024. The Paris Olympics follow in the summer.
Two of Hungarian's main rivals, American Caeleb Dressel and Australian Kyle Chalmers have talked in the last year about their battles with mental health issues, but Milak stressed that was not a problem for him.
"This is a very deep valley, but I want to emphasise that all of this is not accompanied by any despair," he said in the statement.
"I accepted it, and I sincerely hope that everyone else can also accept that in an athlete's career, there can be such a period when you have to step back, recharge, and then be ready for the biggest challenges again."
Milak concluded his statement on a positive note: "Fear not: I will be back soon "