Tennis ace Serena Williams has opened up about her battle against depression while she has been recovering from foot surgery and a consequent pulmonary embolism, which resulted in an operation to remove blood clots from her lungs.

Williams said she had been very unhappy and depressed and found herself crying much of the time while she has been laid up.

Part of her lung 'died' and she remains on blood-thinning medication.  

She is due to have further scans in three weeks to see if the clots are melting.

The star has slipped to world No 11 and is unsure when she will make her comeback but she believes whenever it is, she will work hard to regain her form.