SINGAPORE - Former World No.1 Caroline Wozniacki was diagnosed with rheumatoid arthritis before the US Open. The 28-year-old reigning Australian Open champion revealed the news after the conclusion of her WTA season, which ended with a  5-7, 7-5 6-3 loss to No.7 Elina Svitolina in the final round of group play at the BNP Paribas WTA Finals Singapore presented by SC Global. 

"In the beginning, it was a shock, just you feel like you're the fittest athlete out there, or that's in my head, that's what I'm known for, and all of a sudden you have this to work with," Wozniacki told reporters.

Read more: 2018 WTA Finals Qualification Scenarios: Svitolina, Pliskova set White Group, all to play for in Red Group

"Yeah, it is what it is, and you just have to be positive and work with it, and there are ways that you can feel better so that's great."

"It's been a lot to just take in. After the US Open, I just kind of had to figure out what really was going on. So that's when I really figured it out. I went to see one of the best doctors that there is and, you know, start treatment.

"You know, at the end of the day, it's obviously not ideal for anybody, and I think when you're a professional athlete, it's also not even more ideal, but at the end of the day, you find a plan, figure out what to do, you do your research, and thankfully there are great things now that you can do to it and do about it.

"You just kind of move on from it and work through it and figure out how to deal with it and live with it. That's that. I'm very proud of how I have been so positive through it all and just kind of tried to not let that hinder me."

Wozniacki told reporters she began feeling fatigue after Wimbledon and woke up one morning in Montreal unable to lift her arms over her head and retired from her opening match in Cincinnati. After talking to doctors, Wozniacki was diagnosed with rheumatoid arthritis, an autoimmune disease that causes swelling of the joints and fatigue. She says she's happy to have caught it early.

Read more: Osaka struggles with perfectionism through emotional WTA Finals debut

"I think I didn't want to talk about it obviously during the year because I don't want to give anyone the edge or thinking that I'm not feeling well, but I have been feeling well," Wozniacki said. "You learn how to just cope after matches. Some days you wake up and you can't get out of bed and you just have to know that's how it is, but other days you live and you're fine. You don't even feel like you have it.

"So it's a lot. It's something that now I'm happy that I'm done with the season and you can just kind of control it a little bit more and figure out a plan how to control it even better in the future."

"Some people can go into remission and some people, it just stops, the disease, and it's just right there and it's not going to get worse, or if it does, it's slowly. The medicine now is so amazing so I'm not worried about it. So that's great. You just have to be aware."

Read more: 'Tennis is better than any movie' - Pliskova scouts, spectates in Singapore

Wozniacki said she has been taking medicine and receiving treatment to manage the disease and remained positive that the illness would not significantly impact her career. While her on-court results dipped over the summer - she lost in the second round of five consecutive tournaments - Wozniacki rebounded in Beijing three weeks ago, where she won her third title of the season at the China Open, a Premier Mandatory tournament, and qualified for the season-ending WTA Finals. 

"I think [winning Beijing] meant so much to me," Wozniacki said. "I think you obviously start asking yourself questions, what does this mean, does it mean I can't get in as great of shape as I was before?

"And honestly, the doctor was amazing. She just said, You can do whatever you want to do. You have to feel your body. And a lot of it is also mental. You have to believe in yourself and you have to believe you can do it.

"Obviously winning in Beijing was huge. It also gave me the belief that nothing is going to set me back. I'm going to work with this and this is how it is, and I can do anything.

"I know there are a lot of people in the world that are fighting with this, and hopefully I can be someone they can look up to and say if I can do this, then they can too. And you just kind of have to get together and pull each other up."

Read more: Svitolina stops Wozniacki title defense, surges into Singapore semifinals