Few people know Serena Williams better than her long-time coach.
And if Patrick Mouratoglou is right, Simona Halep may be in strife in Tuesday's Australian Open quarter-final against the 23-times grand slam champion.
Mouratoglou believes Williams, despite closing in her 40th birthday in September, is moving better than she has in years.
He also claims the American is "not as obsessed" with matching Margaret Court's all-time record 24 singles majors than in the past.
Since landing major No.23 at Melbourne Park four years ago while three months pregnant with daughter Olympia, Williams, shackled by her own burden of expectation, has lost four grand slam finals - all in straight sets.
But Mouratoglou says his superstar charge, more relaxed in motherhood, no longer feels a need to validate her place as arguably the greatest player women's tennis has ever seen.
"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."
If she doesn't, Williams' long-time mentor is content that the seven-time Australian Open champion's legacy is secure.
"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."
Of more concern to the Frenchman has been restoring the veteran's on-court athleticism.
"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."
Few players in the game move better than the woman standing between Williams and a place in the last four for a ninth time at Melbourne Park.
Second-seeded Halep trails Williams 9-2 head-to-head, but crushed the American for the loss of only four games in the 2019 Wimbledon final.
The winner this time around will play world No.3 Naomi Osaka or unseeded Hsieh Su-Wei on Thursday for a spot in the final.