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 says.

The world No.1 was knocked out in the third round of the singles at the All England Club before retiring from her doubles, and being 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 that 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 on Wednesday.

“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.