When Serena Williams supporters complain about the bias against her, remember that it's times like these that give her a bad reputation.

Two months after Williams' shocking loss to Roberta Vinci in the U.S. Open semifinals, her subsequent news conference in which she kept anyone from asking about her failed calendar Grand Slam attempt and her disappearance from the game, her coach now comes out and says a knee injury contributed to her loss to Vinci.

WTA Acts Afraid Of Serena Williams

Coach Patrick Mouratoglou said Serena's knees are as gimpy as those that kept Rafael Nadal away from tennis for almost a year, ESPN.com reported.

"It's the same as Rafa," Mouratoglou said. "It's just playing for so many years, the cartilage is [almost] gone. Not all of it, but a big part, so the bones just hit themselves. She has bone bruises, and if you keep on playing with this for too long, too much, the next step is a stress fracture."

Shocking U.S. Open Loss Saps Serena's Motivation To Finish Season

Williams returned to practice this week after taking the extended break that Mouratoglou previously had said was due to Serena's complete lack of motivation to finish the season. She pulled out of the WTA Finals, citing injury.

What's worse is that Mouratoglou now says that the knee injury was as much a part a reason for Williams' breakdown against Vinci as her nerves.

"First, she had pain this day," he said. "With the knees you never know, sometimes the pain is much more [than other days]. That was the first thing she said when she came to the [practice] court: 'My knees hurt so much today.' So she was really struggling to move."

At least, Mouratoglou made sure to include the pressure on Serena to win the calendar slam as a contributing factor.

"I think also the tension went to another level, which I expected, because the closer you get to a final goal, obviously the stress goes to another level. I take responsibility on that because I couldn't find a way to make her handle it better. I think she did incredibly well the whole tournament because she found a way, especially the match against Venus [Williams], because Venus pushed her to play really her best and the level of the match was amazing.

"So I was impressed by the way she was handling it and maybe that's one of the reasons I thought it would be OK. So a bit of both factors, she was not able to play her level and then you know what happened."

It's convenient timing for Serena to return to practice, as she is scheduled to play in two events in the International Premier Tennis League in Japan and the Philippines for a seven-figure payday in December, as The New York Times reported.

Williams, of course, has not spoken to the media since her U.S. Open exit, leaving tennis fans not knowing what to believe about her. As usual. Which always has been why tennis fans have a hard time connecting with her.

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