Serena in 'difficult period', says coach

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".