Venus Williams admits Sjogren's syndrome "takes its toll" on her body

She told Harper's Bazaar magazine: "I had all kinds of symptoms, but that was very challenging as an athlete. When you crash, you go so hard that you can't get up, literally.

"But I still got up, because I had to. Lying in bed is not fun. There is no substitute for being well. I had to change my pace.

"It took seven years before I was diagnosed. It was a head-trip. I wasn't reaching my full potential, and I didn't know why.

"Was I working too hard? What was I doing wrong? That takes its toll and it's not easy to walk out there when you don't have much to give."

In rare cases, complications from Sjogren's can cause kidney problems, uclers, salivary gland infections or pancreatitis.

Some people suffering with the disease could also experience rashes, joint paint, fatique, a persistent cough and other symptoms.

Venus has insisted she plans to keep playing tennis in a bid to "look good" as she encouraged others to take on the sport.

She explained: "I have never neared a burnout, although last week I said I needed a permanent vacation! But I was going too hard for a few months with my schedule.

"That was my decision. We don't always have a choice, but periods of rest are so important. I do weights, and I swim in an Olympic-size public pool near my home surrounded by pines in Florida.

"I'm still training, not every day like before but I'll always need to be on court.

"It's a wonderful way to stay fit, burn calories and have great legs and arms! If you want to look good, play tennis. It doesn't look like work but it's exhausting."

Venus also admitted she hopes keeping up with tennis will delay the effects of ageing.

She added: "I will do that as long as I have cartilage. If I keep playing, hopefully the ageing process won't start."