Ace Kei Nishikori, whose season has been cut short due to injury, dropped from ninth to 10th in the latest men's world rankings released Monday.
It is the first time Nishikori has held a double-figure rank since he was 11th in August 2014.
Nishikori will sit out the remainder of the campaign as he has ruptured a tendon in his right wrist. As a result, he is expected to finish the season outside the top 20.
Nishikori skipped the Western and Southern Open hardcourt tournament earlier this month due to pain in his right wrist before his management announced last Wednesday he was shutting his season down early.
Also for Japan, Yuichi Sugita, who captured his maiden victory on the ATP World Tour at the Antalya Open last month, moved from 46th up to 43rd, matching a personal best.
Spain's Rafael Nadal reclaimed the No. 1 spot for the first time in three years as Britain's Andy Murray dropped to second. Swiss pair Roger Federer and Stan Wawrinka stayed at third and fourth, respectively.