(Photo credit: Robert Deutsch, USA TODAY)

Nine-time Grand Slam champion Monica Seles is battling a new challenge: a neuromuscular autoimmune disease called myasthenia gravis.

The 51-year-old Seles is going public about the condition she was diagnosed with three years ago. It causes muscle weakness in the arms and legs and bouts of double vision among other symptoms.

Seles was noticing odd changes around five years ago and it eventually became apparent to her that something major was wrong.

'I would be playing (tennis) with some kids or family members, and I would miss a ball,' Seles said, according to The Guardian. 'I was like, 'Yeah, I see two balls.' These are obviously symptoms that you can't ignore.

'And, for me, this is when this journey started. And it took me quite some time to really absorb it, speak openly about it, because it's a difficult one. It affects my day-to-day life quite a lot.'

There currently is no cure for the disease.

Seles, of course, had a different hurdle earlier in life as she was stabbed with a knife by a fan during a 1993 match in Hamburg, Germany. Seles was 19 at the time and would be away from the sport for 27 months due to both physical and mental anguish.

Seles won eight Grand Slam titles prior to the stabbing and reached the finals of all four majors in 1992, winning three of them. She won the Australian Open for the third straight time months before the stabbing.

After she returned, Seles won just one Grand Slam title -- the 1996 Australian Open.

'I had to, in tennis terms, I guess, reset -- hard reset -- a few times,' Seles said. 'I call my first hard reset when I came to the U.S. as a young 13-year-old (from Yugoslavia). Didn't speak the language; left my family. It's a very tough time.

'Then, obviously, becoming a great player, it's a reset, too, because the fame, money, the attention, changes (everything), and it's hard as a 16-year-old to deal with all that. Then obviously my stabbing -- I had to do a huge reset.'

Decades later, Seles is now adjusting to a 'new normal' and looking to move forward with the next version of herself.

'Really, being diagnosed with myasthenia gravis: another reset,' Seles said. 'But one thing, as I tell kids that I mentor: 'You've got to always adjust. That ball is bouncing, and you've just got to adjust. And that's what I'm doing now.'

Seles decided to reveal her condition and use her platform to help educate people about the little-known disease.

'My MG journey over the past 5 years has not been an easy one,' Seles said in a statement through argenx, a company partnering with Seles to raise awareness at the upcoming U.S. Open. 'I felt isolated and defeated as many of the activities I enjoyed were no longer physically possible for me. I've since realized that by sharing my story, I can raise awareness of this disease, empower patients to advocate for themselves and help them connect with the MG community for support.'

Seles retired from professional tennis in 2008 and was inducted into the International Tennis Hall of Fame one year later. She won 53 tournaments and spent 178 weeks at No. 1, sixth-most all-time among female players.

--Field Level Media