Caroline Wozniacki has revealed she was diagnosed with rheumatoid arthritis in August and is sometimes unable to get out of bed.

The Australian Open champion spoke of an autoimmune disease which causes swelling of the joints and fatigue after defeat to Elina Svitolina at the WTA Finals on Thursday ended her season.

Wozniacki was unable to lift her arms over her head after waking up one morning following her Wimbledon exit this year and was given a diagnosis ahead of the US Open.

"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," said the Dane.

"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 started treatment."

"It's obviously not ideal for anybody, and I think when you're a professional athlete, it's also not ideal even more, 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."

The world number three added: "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."

"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."

Venus Williams has continued playing at the highest level since being diagnosed with another autoimmune disease, Sjogren's syndrome, back in 2011.