The recent wet weather in London has prevented much practice on grass, so Quayle has been helping to source indoor courts at venues like the Hurlingham Club and the National Tennis Centre.
“The practices we have been having have been pretty special,” Quayle continued.
“She’s not lost it – she’s still operating at a very high level. She is just the ultimate professional.
“For me, she’s the greatest of all time, and you see that in the way she does things on the court.
“It’s incredible to just be a part of and witness – never mind to actually be learning from her and seeing her as a friend and an opponent.”
Despite being a well-established hitting partner on the professional tour – and with a job already lined up at Wimbledon – Quayle says his first few practice sessions with the 23-time Grand Slam singles champion made him “a little bit nervous”.
“It’s a funny thing to see someone that you have watched their serve on TV for so many years, and then all of a sudden that serve is coming at you,” he explained.
“You’re fighting between admiring some of the shots and actually playing them. She’s got that kind of aura and it’s hard sometimes not to feel a little bit nervous.
“I’m starting to getting a little bit more used to seeing her over the other side of the net, but every day is special.”
Quayle, who would one day like to move into coaching, is encouraged to speak up if he has observations about the way Williams is training.
He praised the environment around her, saying the team are “easy to get along with”.
“She’s got a lot going on off the court so we don’t spend a lot of time outside of the gym or the practice court, but when we’re together, she’s so nice,” Quayle said.
“She’s so welcoming. We’re always cracking jokes and we’ve got a similar sense of humour.
“Everyone in that team makes it such a nice environment for everyone.”
Quayle has been asked to head on to Berlin next week, where Williams will play the second tournament of her comeback with a partner yet to be announced.
He says he does not yet know whether his boss will be playing at Wimbledon, which begins on Monday, 29 June, but he is at least relieved he no longer needs to be quite so vague to friends about his movements.
“I feel like I can breathe and relax a little now the secret is out there,” he added.