PARIS • Serena Williams' coach says her recent break was down to the fact that she was suffering from depression and she also needed to allow her knees to recover after missing out on the calendar Grand Slam in September.

"She was depressed," Patrick Mouratoglou told ESPN. "The reaction was quite strong. She was really, really affected, which I think is normal when you are Serena.

"She does everything with 100 per cent of her heart, so you are more disappointed when you don't reach your goal. Plus, she has a level of expectation that is much higher than anyone."

Williams had been unexpectedly beaten in the US Open semi-finals by Roberta Vinci when it appeared that the "Serena Slam" was a guaranteed bet and Mouratoglou said that they did not speak for two weeks afterwards while he allowed her to get it out of her system.

"She doesn't want to talk when she's depressed," he said in Paris. "But it's better. Because I represent tennis, and when you are (recovering) after something like this, you have to see people who don't represent tennis.

"You have to change your mind. Otherwise you keep on thinking about it. I didn't force it. I know her and I understand also that she needs a break. It's fine."

The coach also disclosed that Williams is plagued by knee injuries similar to those that have hindered the career of Rafael Nadal.

"It's the same as Rafa," Mouratoglou said. "It's just playing for so many years, the cartilage is 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."

Mouratoglou said the break had given the injuries a chance to heal.

"There was no other option," he said. "The injury can get really worse, and at her age her career could really be in danger if she went too far and got more injured, like Rafa did in the past...

"She is 34, if she has to stop for a year then it is really bad for her future."

THE GUARDIAN