Former world number one Caroline Wozniacki says she was “shocked” to be diagnosed with rheumatoid arthritis, but wants to become a role model for people with the condition.

The Dane, 28, discovered she had the auto-immune disease in August and says “it has been a lot to take in”.

Rheumatoid arthritis causes pain, swelling and stiffness in the joints.

“You feel like you’re the fittest athlete out there and all of a sudden you have this to work with,” she said.

• Wozniacki knocked out of WTA Finals by Svitolina

Wozniacki – who won the Australian Open in January, her only Grand Slam to date – revealed she had the condition after her season ended with defeat at the WTA Finals.

She said she began to notice symptoms of fatigue after Wimbledon, where she lost in the second round, and one morning was unable to lift her arms over her head.

The world number three says some days she has struggled to get out of bed and doctors diagnosed her in August before the US Open.

“In the beginning, it was a shock,” said Wozniacki. “It’s obviously not ideal for anybody, and I think when you’re a professional athlete, it’s also not even more ideal.

“I think I didn’t want to talk about it 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.”

Rheumatoid arthritis can affect people of any age, although often starts when a person is between 40 and 50. It occurs when the body’s immune system targets affected joints, leading to pain and swelling.

The NHS says there is no cure for the condition, but medication and other treatments can relieve symptoms.

Wozniacki has been taking medicine and receiving treatment to manage the disease and is positive the condition will not impact on her career – she won the China Open earlier this month.

“I think [winning in Beijing] meant so much to me,” she added. “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?

“Winning 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’m very proud of how I have been so positive through it all and just kind of tried to not let that hinder me.

“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 that if I can do this, then they can too. And you just kind of have to get together and pull each other up.”

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British number one Kyle Edmund is out of the Vienna Open after losing to Spain’s Fernando Verdasco.

The 23-year-old lost the second-round match 6-4 3-6 6-3 in two hours.

It brings to an end Edmund’s five-game winning run that included his maiden ATP Tour title at the European Open.

Verdasco broke twice in the first set to take the lead before Edmund broke early in the second to level the match, but one break of serve was the difference in the decider.

World number 14 Edmund will now head to Paris for the final Masters tournament of the season, where victory would give him an outside chance of qualifying for the ATP Finals.

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Karolina Pliskova defeated Czech compatriot Petra Kvitova in straight sets to secure her place in the semi-finals of the WTA Finals in Singapore.

World number eight Pliskova, 26, won 6-3 6-4 for her first victory over Kvitova, 28, in four attempts.

It is the second successive year former world number one Pliskova has reached the semi-finals at the season-ending tournament.

“I cannot be more happy right now,” said seventh seed Pliskova.

“It was a good match and she’s a great player. She has always beaten me in the past but I knew I had a chance as I have been playing well.”

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Kvitova – the WTA champion in 2011 – lost all three round-robin matches and will finish bottom of the White Group.

Defending champion Caroline Wozniacki and Elina Svitolina will contest for the second semi-final berth later on Thursday.

Two-time Wimbledon champion Kvitova needed to win in straight sets to stand any chance of reaching the semi-finals but Pliskova dominated the opening exchanges, racing into a 4-0 lead following a string of double faults from Kvitova.

Though she went on to win back-to-back games, Kvitova’s tournament was ended as Pliskova held serve to take the first set in 41 minutes.

With the pressure off, Kvitova took the first three games of the second set and went on to lead 4-2 before Pliskova won four consecutive games to round off the win.

Sloane Stephens beat Kiki Bertens at the WTA Finals, in a result that spared US Open champion Naomi Osaka early elimination.

The American, 25, won six of the last seven games to claim the match 7-6 (7-4) 2-6 6-3.

The victory means all four players in the Red Group can still qualify or be eliminated going into the final games.

Osaka has lost both her round-robin matches, but can progress if she wins and the other result goes her way.

In Friday’s final round of fixtures, Osaka plays Bertens while Stephens faces Angelique Kerber, who beat Osaka earlier on Wednesday and has one win from two.

Stephens and Bertens, 26, traded breaks throughout in a match which saw momentum change regularly.

Fifth seed Stephens won the first-set tie-break, before Bertens broke three times in the second set to win it in 36 minutes.

The third set continued the trend as the Dutchwoman won the first two games before Stephens took the match away from her. The 25-year-old now has two wins from two in the group stage, while Bertens has one.

• WTA Finals: Everything you need to know

Earlier on Wednesday, Kerber beat Osaka 6-4 5-7 6-4 in a match that included 11 breaks of serve.

Germany’s Kerber, 30, won the first set and was a break up at 5-4 in the second, but the Japanese fought back to level the match. Kerber then won the final set to clinch the match, which lasted 2 hours and 31 minutes.

There is a similar situation in the White Group, in which Elina Svitolina, Karolina Pliskova, Caroline Wozniacki and Petra Kvitova can all still qualify after two matches.

The WTA Finals feature the top eight players this year, split into two groups of four. The top two from each group progress to the semi-finals, with the final on Sunday.