Coach's bombshell theory on Serena Williams retirement

Serena Williams is not done with tennis and won't retire from the sport until she wins another grand slam, according to her coach.

Speculation has swirled over the last week that this year's Australian Open campaign was Williams' last, and that her retirement from the sport was imminent.

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Serena waved a long and emotional goodbye to fans at Melbourne Park after being eliminated by eventual champion Naomi Osaka in the semi-finals, before leaving her press conference in tears a short time later.

Many tennis fans and experts took it as a sign that the 39-year-old was on the verge of announcing her retirement from the sport, something the American insisted she wouldn't reveal even if she was.

Commentator Sam Smith said she'd never seen Williams break down like she did in her press conference and insisted that "she won't be back" to Melbourne Park.

However, the 23-time grand slam champion's coach Patrick Mouratoglou has offered Aussie tennis fans a glimmer of hope that the popular champion will return.

Mouratoglou - who has coached Williams since 2012 - says he can't see the 39-year-old calling time on her career until she wins that elusive 24th major title to equal Margaret Court's all-time record.

"I don't think she will stop until she at least wins a grand slam, because she came back to win Grand Slams," Mouratoglou told People, referring to the American's comeback after giving birth to daughter Alexis in 2017.

"She doesn't quit," he added.

Serena's coach says he understands why the American - who turns 40 later this year - would be loathe to contemplate, let alone discuss retirement from a sport she has dedicated her whole life to.

'Dedicated all her life to tennis'

"I don't think she planned [retirement] for this certain moment. She's dedicated all her life to tennis since she was a kid," Mouratoglou says.

"So the day she will retire, she will feel like she's giving an end to 40 years of a life."

"It's something that is difficult to measure for people.

"That's why it's very sensitive. That's why it's very emotional for her. I completely get it."

The American's coach says her "exceptional" mentality and impossibly high standards fill him with every confidence that Williams can claim that record-equalling grand slam title, before she hangs up the racquet.

"I have to believe it and she has to believe it, too. If she [doesn't], she would stop.

"After all she's achieved in her career, at her age, having a baby for the first time, having a family — it was an incredible effort to come back to tennis," the coach tells PEOPLE.

"Unbelievable effort. Mental effort, physical effort, so many hours to get back in shape. She would never even start that if she didn't think she was able to win a grand slam.

"That's how Serena is really exceptional. She puts the standards so high for herself, and she finds a way to match those standards, whatever she does."

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