London: Serena Williams' coach has revealed that the world number one ended this year's season prematurely as she was suffering from depression caused due to the US Open loss and said that she needed time to recover from her knee injuries.
Speaking on the matter, coach Patrick Mouratoglou informed that Serena had been suffering from bone bruises and it could have worsened if she had continued to play with injury, the Guardian reported.
Earlier, Roberta Vinci of Italy had crushed Serena's hopes of completing a calendar grand slam by claiming a 2-6, 6-4, 6-4 win at the Flushing Meadows.
Expressing his views on the American's loss, Mouratoglou said that Serena was quite affected by the loss, pointing that the player had higher expectation from herself.
According to Mouratoglou, the star player should be given some time to overcome the situation.
The 21-time Grand Slam champion had earlier missed both China Open and the WTA Finals in Singapore.
Serena has won three Grand Slams this season -- the Australian Open, the French Open and Wimbledon.