Kamau Murray had a message for his charge Sloane Stephens when she called him five months ago - "Let me know when you can walk."
Following surgery, Stephens was not allowed to put any weight on her foot for 16 weeks. She began hitting tennis balls sitting on a chair. Two months after her first tournament back, she won the US Open.
The story, Stephens said on court following her 6-3 6-0 trouncing of fellow American Madison Keys in the final, was impossible.
Yet there she was, lifting her first grand slam trophy on home soil and, with wide-eyed incredulity, collecting a cheque for 3.7million US dollars (Â£2.8million).
Stephens had plateaued after reaching her first grand slam semi-final at the Australian Open in 2013 before turning to Murray ahead of the 2016 season.
The former college player combined his coaching with a corporate job in pharmaceuticals until two years ago when he decided to go full-time.
He also established a foundation in Chicago teaching tennis to underprivileged children and it was Stephens' enthusiasm for that project that convinced him she was a player he wanted to work with.
There were positive signs prior to the stress fracture that sidelined her last August but neither could possibly have imagined how quickly major success would come.
A key factor has been the sheer joy Stephens has found in simply being able to play tennis again.
"I think she has remained positive throughout the process," said Murray. "You get the game taken away from you and then you come back, you start to appreciate it more.
"She legitimately loves to play tennis. She would call me, and she was all, 'I can't wait to get back on the court'. I was like, 'Really? I'm enjoying my kids now, let me know when you can walk'."
Stephens dealt with the inevitable nerves of a first grand slam final significantly better than Keys, her close fried and former junior rival, who was never able to settle into her game.
"I was surprised," said Murray. "That's a nerve-wracking experience to walk out there. But I thought she handled it well.
"To her credit she spoke up the night before and in the gym, 'Wow guys, I'm a little nervous, but let's go do this'. I think her evolution as a person is to communicate very clearly and honestly."
Now the 24-year-old must deal with the inevitable attention and pressure that comes with being a grand slam champion.
Stephens had a taste of it four years ago when she defeated Serena Williams to reach the last four in Melbourne.
She has also been through a lot in her young life, including the deaths of both her father and stepfather when she was a teenager.
"A lot of life has happened, a lot of good things and bad things have happened," she said.
"Every time you do something big it's going to be different, so I'm sure now that I've won a grand slam things are going to be way different than making the semi-finals like I did before. I'm ready and prepared and I think my team and everyone around is excited.
"I'm not going to change much, I'm going to try and keep everything like I have before. Obviously there's going to be more responsibilities and a lot of other things I have to do.
"There's always going to be struggles. I'm adding a lot more to my life. I'm sure there will be some ups and downs and some tough times. I'm actually looking forward to it. It will be challenging but super fun."
Stephens' victory capped a year of change on the WTA Tour, with the last three grand slam titles all won by players under 25.
The US Open, meanwhile, comprehensively belonged to America - the host nation boasted all of the semi-finalists for the first time since 1981.
Fourteen of the world's top 100 represent the United States, easily the highest number of any country, and that could soon increase.
The last three junior slam finals have been all-American affairs, with the US Open final featuring Amanda Anisimova and 13-year-old Cori Gauff, the youngest finalist in the event's history.