Former world No. 4 Kei Nishikori has tumbled out of the top-100 in men's tennis for the first time in 12 years, according to the latest ATP singles chart released Monday. Nishikori, who has been sidelined following left hip surgery in January, slipped from 84th to 104th, two places back of Japanese compatriot Yoshihito Nishioka. The last time Nishikori finished outside the top-100 was in Nov. 15, 2010, when he was ranked 101st. Russia's Daniil Medvedev replaced Serbian star Novak Djokovic at the top of the ATP Tour rankings.