Earlier this week, the 18-year-old swim queen tweeted that she had cut short a training camp in Australia after feeling unwell and had been diagnosed with the illness on her return to Japan.
The news sent shockwaves around the sport and well-wishes have flooded in for Ikee, a genuine title contender at the 2020 Olympics in her home city.
"I was shocked," two-time world champion Daiya Seto said at the Konami Open in Tokyo on Saturday. "With the Tokyo Olympics on the horizon, people will no doubt be urging her to get well and compete.
"But obviously life is more important," added the Rio Olympic bronze medallist. "I just pray she gets better soon and we can see her cute smile again -- all we can really do is pray."
Ippei Watanabe promised to break his own world record in the men's 200m breaststroke at the Japanese championships in April to help encourage Ikee in her battle to recover.
"I'm confident of setting a new world record," he said. "Hopefully that will offer her a little encouragement at least." Ikee, who shot to fame by capturing a record six gold medals at last year's Asian Games, was a genuine contender to win the women's 100m butterfly at the Tokyo Olympics and tipped to push hard on several other fronts.
- Bombshell news -
But her bombshell announcement has left her fellow swimmers stunned. "It looked as if she was really struggling," said Suzuka Hasegawa, who was also training on Australia's Gold Coast when Ikee's health problems began.
"We went shopping together in our free time and I couldn't have imagined she was sick. When she left (Australia), she just told me she had to leave early. I couldn't believe it when I saw the news. We will all have to put in an extra shift while she's away."
Sweden's Sarah Sjostrom, Olympic champion in the women's 100m fly and expected to be Ikee's rival for the gold medal next year, posted:
"My eyes are filled with tears when I read the news about my friend (Rikako Ikee) being diagnosed with leukaemia. Sending all my strength and love to you!"
Hollywood actor Ken Watanabe, who survived acute myeloid leukaemia in the 1990s, also tweeted a message of support for his countrywoman. "You may be feeling desperate," wrote the Last Samurai star.
"You might be wondering 'Why me?' I hope you will be positive and concentrate on the treatment, trust in your life force."
Doctors believe they detected Ikee's leukaemia in its early stages. The swimmer, who has been hospitalised in Tokyo, tweeted: "If treated properly it's a disease that can be beaten. I will devote myself to my treatment and strive to be able to show an even stronger Rikako Ikee."