[9] Madison Keys had to miss the first Major because she had arthroscopic left wrist surgery during the off-season (12/2016).

[12] Petra Kvitova is recovering from left hand surgery after she was attacked with a knife during a home invasion in December, 2016.   She hopes to make a successful recovery and return to the Tour later this year.  We wish her a speedy recovery.

[19] Victoria Azarenka is missing from the Tour not because of illness, but because she gave birth to a son in December last year.

[38] Juan Martin Del Potro did not play in the first Major of the season, citing concerns about his fitness; however, given the amount of tennis he played late last season, he probably wants to protect his wrists that are still a concern despite numerous surgeries.

[46] Nicolas Almagro has not played since his first round withdrawal due to left calf injury at the Australian Open. His quick withdrawal caused a stir about unsavory reasons for showing up and only playing 23 minutes. Almagro negated the suggestions and claimed his MRI result was not good and since he was expecting the birth of his first child, he would miss some upcoming tournaments to heal as well as enjoy fatherhood.

[50] Sloane Stephens had to miss the Australian Open because of an issue with her foot, the plan was to have surgery to correct the problem, which she did on her left foot at the end of January.

[72] Catherine Bellis withdrew from the Australian Open due to hip injury.  This is troubling given the fact that she is so young in her career and injuries at this stage bodes ill if they do not heal properly.

[?] Maria Sharapova is still serving the term on her suspension due to the use of the banned substance, Meldonium.  She is expected back on Tour at the end of April.

Injury is the one opponent many tennis players hope to avoid in their career; unfortunately for so many, that is not possible.  Several players (Robin Soderling, Dinara Safina, et al) ended their careers because of illness or injury they never recovered from, either physically or mentally.  I have always believed that Monica Seles never got back to her top form after that stabbing in the upper back because she never fully recovered psychologically from that unfortunate trauma.

SOURCE OF IMAGE: Bing search