As the US Open approaches, anticipation is sky-high to see who captures the final slam of the year. Players are sharpening their styles, but Coco Gauff? She’s looking to flip the script. After a rollercoaster 2025 season, where she won just one title, the French Open against World No.1 Aryna Sabalenka, her form has been under the spotlight. Since that final in Paris, early exits have fueled scrutiny of both her performances and her coaching team. But in New York, it looks like she’s decided to shake things up and bring the heat.

On Wednesday, 2023 US Open champion and 2025 Roland Garros winner Gauff announced a bold move. She split with coach Matt Daly and added biomechanics expert Gavin MacMillan, as reported by ESPN. MacMillan, a former San Jose State tennis scholar and founder of Sport Science Lab in 2001, once worked with Aryna Sabalenka to fix her serve. Now, he’s courtside with Gauff at Arthur Ashe Stadium, standing next to JC Faurel, who continues to guide her.

Is this the right call? History leans, yes. Almost exactly a year ago, Coco Gauff made a similar switch. Just before the Asian swing, she split with longtime coach Brad Gilbert and joined forces with Daly. The move drew plenty of skepticism at first. But Gauff quickly silenced the doubters.

She charged into the China Open and snapped a nine-month title drought. Then, she capped her season by lifting the WTA Finals trophy. It was a stunning turnaround for a teenager trying to steady herself after her early-year win at the ASB Classic. Could MacMillan spark another revival? The stage is set, and once again, only time will tell if Coco’s move pays off.

On the other hand, Darren Cahill, Jannik Sinner’s current coach, opened up about this collaboration. “A lot of things add up and this could be a really good relationship,”  he said, “He’s very thorough ….I’ve spoken to him many, many times before and the fact that he’s got experience with different athletes from different sports, both male and female, he uses the new technology, he goes to the video a lot, really breaks down the biomechanics.” 

But could he help Gauff with her problem areas on the court? Tennis legends like Rennae Stubbs have been honest about their thoughts on the American’s form lately.

Stubbs calls out Coco Gauff’s coaching team for her form

Gauff’s recent stumbles at Washington, Montreal, and Cincinnati have fueled more scrutiny of her game, especially her serve. Serena Williams’ former coach Rennae Stubbs has long flagged this as a concern, previously warning that Gauff’s serve “is going to be a problem for her forever” unless addressed fast. Seeing her rack up more than 10 double faults in almost every match, Stubbs admitted she was shocked. To her, those numbers were simply “unheard of.”

The warning rang louder after her early Canadian Open exit to 18-year-old Victoria Mboko. On 5 August, during The Rennae Stubbs Tennis Podcast, she praised Gauff’s talents before drilling into the flaw holding her back. “My God, like her serve, I don’t understand why now she has literally two coaches. Nothing has changed on her serve… like the ball toss is so far ahead of her on the second serve.” For Stubbs, it isn’t just the toss. She insists Gauff needs a sharper kick serve and believes her grip looks “messed up a bit” and “too far around.”

The numbers in Canada backed her up. Coco Gauff hit 23 double faults in her loss to Danielle Collins, tying the fifth-highest tally ever in a WTA match. Frustrated, she promised to “come back stronger in the next round.” But her next outing wasn’t much better. Against Veronika Kudermetova, she committed 14 more double faults before pulling out a 4-6, 7-5, 6-2 win. In total, that’s 37 double faults across just two matches.

Things didn’t improve much in Cincinnati either. In the quarterfinals, Jasmine Paolini outlasted her in a 2-6, 6-4, 6-3 win despite rolling her ankle mid-match. While the Italian held firm, Gauff’s stats told the story—16 double faults compared to Paolini’s two, a shaky 54% first-serve percentage, and 62 unforced errors to Paolini’s 44.

The question now is: can her new partnership with biomechanics expert Gavin MacMillan, the man who helped Sabalenka clean up her serve, finally fix Coco’s biggest weakness? Let us know your thoughts in the comments below!