What is myasthenia gravis?

The Serbian-American, 51, was diagnosed with myasthenia gravis (MG), chronic neuromuscular disease, three years ago.

"I would be playing with some kids or family members, and I would miss a ball. I was like, 'Yeah, I see two balls',” she told Associated Press of the first signs of the condition.

"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."

Seles, who won nine grand slam titles in her career, has not played professionally for more than 20 years but remained active in her retirement.

She said she is now getting used to living with myasthenia gravis and is trying to raise awareness of it.

"One of the reasons I decided to go public with my myasthenia gravis (is) because it's been a huge reset in my professional life as a tennis player, also in my personal life," she said in an interview with Good Morning America.

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What is myasthenia gravis?

Myasthenia gravis is a rare long-term condition that causes muscle weakness, the NHS states.

“It most commonly affects the muscles that control the eyes and eyelids, facial expressions, chewing, swallowing and speaking. But it can affect most parts of the body,” a write-up said.

Seles said her symptoms included extreme leg weakness, arm weakness, and double vision.

Other symptoms include droopy eyelids, problems swallowing, and shortness of breath.

“The symptoms tend to get worse when you're tired. Many people find they're worse towards the end of the day, and better the next morning after getting some sleep,” the NHS adds.

It is a long-term condition and there is no cure but sufferers are able to take medicines for some of the symptoms and also avoid other triggering activities.

Seles added: "Once I was diagnosed, it was like a relief, but also it was a challenge. Even coming here today... in the old days, travelling would be a no-brainer. Now I had to get packing tips. I had to learn a new way to live with MG.”

Who is Monica Seles?

The Serbian-born American was only 19 when she won her eighth grand slam title in Australia in 1993 and seemed destined to become the greatest of all time.

However, that year she was stabbed by a spectator during a match in Hamburg and was in hospital for a period, going on to experience depression and an eating disorder.

She returned to tennis and won the Australian Open for a fourth time in 1996, changing nationality in 1994 to the US.

• Age: 51
• Nationality: Yugoslavia (1972-1994), US (1994-present)
• Grand slams won: Nine (Australian Open 1990, 1991, 1992, 1993, 1996; French Open 1990, 1991, 1992; US Open 1991, 1992),
• Retired from tennis: 2008, although last match in 2003,
• Married to: Businessman Tom Golisano, since 2014
• Political party: Undeclared, although Mr Golisano has been a Republican since 2005