Citing the continued erosion of her ailing knees, two-time Grand Slam winner Li Na announced her retirement from professional tennis in a lengthy statement released on her official Facebook page … http://bleacherreport.com/articles/2203832-li-na-announces-retirement-from-professional-tennis-latest-comments-reaction?utm_source=cnn.com&utm_medium=referral&utm_campaign=editorial&hpt=ias_c2
