However, Mouratoglou refuses to elaborate on star's Wimbledon collapse

Serena Williams, whose Wimbledon campaign ended with her in tears and on the verge of fainting, is enduring a "difficult period" in her life, her French coach said on Wednesday.

The world No 1 was knocked out in the third round of the singles at the All England Club before retiring from her doubles; where she had to be led off the court by sister Venus with her problems attributed to a "viral illness".

Although her coach, Patrick Mouratoglou, refused to discuss the American's current mood, he did admit the 32-year-old was facing a series of challenges in a season where she has yet to get beyond the fourth round at any of the Grand Slams.

"Serena is clearly going through a difficult period. But since Wimbledon, we have had long hours of talks and we are getting back to work," Mouratoglou told tennismagazine.fr.

"Today she is in the mood to get back to training so she can return even stronger. At no time was there any question of us stopping our collaboration."

Mouratoglou, who has long been romantically linked with Williams, refused to elaborate on any problems the American was suffering or if the two had split either personally or professionally.

"I have never discussed private matters and I am not going to talk about them now. There have been difficult things. For sure, Serena is in a difficult phase but I will leave it there."

Williams is due to return to action at the Stanford event in California from July 28.

Serena also heads the women's field for the US Open, which starts in New York in late August.

Players from 36 countries and regions are represented, the US Tennis Association announced on Wednesday, with two-time defending champion Williams heading an 11-strong American contingent for the Aug 25-Sept 8 event.

Williams has five US Open crowns, just one shy of the modern era record held by compatriot Chris Evert.

Joining Williams in the top four are Li Na of China, Simona Halep of Romania and this month's Wimbledon champion, Petra Kvitova of the Czech Republic.

The field also includes French Open champion Maria Sharapova, two-time US Open champion Venus Williams and former US Open champions Samantha Stosur and Svetlana Kuznetsova.

The latest WTA rankings were used to determine the main draw entry list for the final Grand Slam event of 2014 but seeds will be announced closer to the event.

(China Daily 07/18/2014 page24)