Serena Williams'  Grand Slam dream was shattered with a US Open semifinal loss. The world No. 1 returned to practice yesterday armed with a new dream: Winning the 2016 Grand Slam.

Patrick Mouratoglou, Williams' coach, said Serena is scheduled to start a six-week training session at his academy in Nice next month. In an interview with Rohit Brijnath of The Straits Times, Mouratoglou said "of course" the 21-time Grand Slam champion is striving for the calendar Grand Slam in 2016.

More: Sharapova Not Impressed with Rivals Support of Serena

"At the start of 2015," Mouratoglo told The Straits Times, "journalists asked me what is the goal. I said to win four Grand Slam (titles). They said this is crazy. I said this is not crazy. She won four in a row, not four in a year, but she was two matches away.

"Of course (the goal is the same)."

The 45-year-old Frenchman suggested spiking stress from trying to complete her Grand Slam quest and creaky knees contributed to Williams' loss to Robert Vinci in the US Open semifinals. Mouratoglou says he takes the blame for his inability to calm Williams' nerves before the semifinals.

"Obviously she didn't play her level so I should have felt that before the match and I should have found a way, speaking to her, that she would play better," Mouratoglou told The Straits Times. "I think she had pain in her knees because that was the first thing she told me in the morning — 'My knees are killing me today.'

"Also because she was two matches away from the Grand Slam (and) the stress went to another level. I should have felt it and should have talked to her in a way so she would have dealt with it better."

Mouratoglou says Serena's serve, mental strength, power and longevity make her the greatest player of all time.

"(She is the greatest) because she is the strongest player mentally of the history," the coach told The Straits Times. "Because she has the biggest serve of the history. Because she has the most power of the history. Because she is able to win Grand Slams (over) 17 years, having to face so many different types of players... and every time she found a way to win. Because she's 34 and she is still No. 1 and won four Grand Slams in a row.

"I am sure if I think I can find 10 more reasons."