The 25-year-old American, who reached the quarter-finals of her home Grand Slam earlier this month, said in an Instagram post on Wednesday that she aims to be back for next year's Australian Open.
"I have learned that there is no weight on the scale or leanness in your limbs that is more valuable than your health or your well-being," she wrote.
"I am taking the rest of this year to work on dialling in my medication and fueling protocols so that I can hopefully feel back to 100% again."
RED-S is a condition that leads to the body not receiving enough energy for heavy physical activities typical for athletes, while Hashimoto's hypothyroidism is an autoimmune disorder where the immune system attacks the thyroid gland, causing slower metabolism.
Navarro, who reached a career-high ranking of world number eight two years ago, said she had been experiencing increased hunger and a weakening immune system since 2023 but pushed through it to keep up with the busy tennis calendar.
She fought through headaches, dizziness and heavy fatigue during her run to the quarter-finals of the 2025 Australian Open, and did not figure out what was causing them until doctors diagnosed her in November that year.
"So over the past year, I have gone all in. Changing my diet, increasing my energy intake... although it took a while to start feeling better, I gradually made progress," Navarro wrote.
"So yeah. I gained some weight this year. But I also gained my life back. I have enough energy to seize every day, to train or compete as hard as I want to, and to live a life outside of tennis."