5, Justine Henin
After her third-round exit at the 2011 Australian Open, the former World No. 1 player announced her definitive retirement from professional tennis on 26 January 2011.
Henin cited a recurrence of the elbow injury she had previously suffered the year before at Wimbledon. Henin originally retired in 2008, only to make a comeback at the 2010 Brisbane International.