Maria Sharapova could have won at least 10 grand slam titles if she had not suffered a shoulder injury that took away "one of her biggest weapons", Michael Joyce believes.
Sharapova retired last week aged 32, revealing her body had become a "distraction" after being troubled by injury problems for much of her career.
The former world number one was out for nine months following a first operation in 2008 and coach Joyce had to work on remodelling the Russian's powerful serve in order to prolong her career.
Sharapova won the French Open twice following her return to take her major haul to five and complete a career Grand Slam, but could not add to that tally after a 2014 triumph at Roland Garros.
Joyce, who coached the global icon from 2004 to 2011, says it was a huge achievement just to come back from the surgery early in her career and is sure there would have been more major glory if she had not been so unfortunate with injuries.
He told Stats Perform : "What a lot of people don't realise is her coming back from that shoulder surgery was a win itself.
"We tried to do everything to not have surgery, but it got to a point where nothing we did was helping her.
"When the doctors went in I was there with her and the doctor came after about 30 minutes and said, 'Listen, I couldn't really do much, she had a tear in her rotator cuff, the way her shoulder is built I could have tightened it up, but then she could maybe not ever serve again'.
"He said he just cleaned it out, but told me I am the coach and have to figure out when she comes back if there is something mechanically she is doing or whatever.
"We'd had about a year of changing her service motion and trying different things, she went through a period where she was double-faulting, so people were questioning what we were doing and why she couldn't get the serve in.
"She had a great serve, but at the time her shoulder wasn't strong enough to do her normal long motion. She got back to the top 10 basically without one of her biggest weapons.
"The rest of her career I think she managed it, she could still serve big but I don't personally think it was anything like before she had the injury. I think if she hadn't hurt her shoulder she could probably have won double-digit grand slams.
"For her to come back and win the French Open a couple of times, because clay was her worst surface when she was younger, was because the serve is not as important on clay.
"For somebody to transform their game in a way to win more grand slams on their worst surface is incredible, it shows her resilience and determination."
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