Robin Soderling of Sweden reacts during his match against Lleyton Hewitt of Australia at the Wimbledon tennis championships in London, June 23, 2011. [Photo/Agencies]

Venus Williams of the US reacts to a point during her first round match against Vesna Dolonts of Russia at the US Open tennis tournament in New York, August 29, 2011. [Photo/Agencies]

BEIJING - Swede Robin Soderling and American Venus Williams have pulled out of the China Open due to illnesses, organizers confirmed on Saturday.

Soderling has said earlier this month that he was suffering from mononucleosis, also known as the kissing disease, which explained his extreme fatigue and that kept him out of contention at the US Open.

The disease is fairly common among tennis players, with the likes of Roger Federer, Andy Roddick and Mario Ancic all having suffered from it at some point in their careers.

It is unclear how severe Soderling's case is, but if it is serious he might not play again this year.

Another major blow for the local organizers came from the former world number one Venus, who was diagnosed with Sjogren's Syndrome that causes fatigue and led to her decision to withdraw from the US Open too.

"It's a pity that I have to skip Pan Pacific Open in Japan and the China Open. I've always enjoy those tournaments in Asia," Venus said in an email sent to the organizers.

"I'm working hard on recovery, and I could see the progress so hopefully I can get back to the court next year," the seven-times Grand Slam winner added.

Sjogren's syndrome can lead to inflammation in the muscles and lungs,  make patients feel lethargic and cause dryness in the mouth and eyes.

Although Sjogren's syndrome isn't life-threatening, it is an incurable condition where the immune system starts attacking glands that produce tears and saliva instead of fighting infection.