Serena Williams' coach makes stunning claim about Margaret Court

The later stages of Serena Williams' career have been somewhat defined by her quest to equal Margaret Court's record of 24 grand slam wins - but her coach says it isn't her main driving force.

Williams has won 23 grand slams, and impressive feat in the modern era in which she has dominated, but equalling the all-time record is an achievement that has thus far eluded the 39-year-old.

'IT'S IMPOSSIBLE': Nadal's pointed response to Djokovic injury saga

'FED UP': Pregnant ex slams Aus Open star's baby 'lies'

Her most recent grand slam triumph was 2017 Australian Open, which she memorably won while pregnant with her daughter Alexis.

Though Williams is well-positioned for another deep run at Melbourne Park, advancing to a quarter final matchup against Simona Halep, her long-time coach Patrick Mouratoglou says she isn't motivated by equalling Court's record.

"Clearly she came back to tennis to win some other grand slams, so that's for sure the goal, but now she's not as obsessed with the 24 than most of the people in the tennis world," he said on Monday.

"But definitely she wants to win grand slams. That's the only reason why she came back to tennis."

Mouratoglou argued Williams' 23 grand slam wins in the Open era compared well to the amateur era, arguing the different eras amounted to playing 'two different sports'.

Despite this, the French coach admitted it was fun to think about the prospect of breaking records.

"There is tennis before the open era and tennis after the open era. We all know it's two different sports," Mouratoglou said.

"It's an amateur sport and a professional sport. Doesn't make really sense to compare.

"But it's probably fun to talk about beating records, which is something that I understand."

Conditioning key to Serena Williams' Australian Open run

After injuries stymied her attempts at grand slam glory over the past few years, Mouratoglou said Williams was in the best shape she'd been in for some time heading into the Australian Open.

While there was no taking away Williams' knowledge of the game, Mouratoglou admitted her lateral movement had suffered as her career went on.

"For sure she is moving better than the last three years. No doubt about it," Mouratoglou said.

"It's something that we have put the emphasis on because in tennis that's probably one of the most important things.

"If you are late on the ball, you can't do what you want to do. Sometimes you don't even touch the ball.

"It's a sport where you have to be able to move fast from side to side and long enough.

"It's something that probably in the last two, three years, this had consequences for Serena.

"If you can't move well, there is no Plan B. The only plan is attack.

"I think it cost her a few important matches."

With AAP

Click here to sign up to our newsletter for all the latest and breaking stories from Australia and around the world.