Kei Nishikori at the 2020 Summer Olympics, on July 29, 2021, in Tokyo, Japan. (Mainichi)

       TOKYO (Kyodo) -- Kei Nishikori was forced to withdraw from the National Bank Open in Toronto with a shoulder injury on Wednesday, hours before his second-round match against Hubert Hurkacz of Poland.

       Nishikori, currently ranked 55th in the world, has been in a good run of form recently amid a very up-and-down season. The 31-year-old Japanese lost to Serbian world No. 1 Novak Djokovic in the men's tennis singles quarterfinals of the just-ended Tokyo Olympics.

       "I am disappointed to announce that I have decided to withdraw from my match today," Nishikori said in a statement.

       "The right shoulder is very sore after a long stretch of tennis and I do not want to risk further injury. I now spend my focus on getting healthy back on court again."

       Nishikori started his campaign in Toronto by beating Miomir Kecmanovic of Serbia 6-4, 6-7(5), 6-2 in the ATP Masters 1000 event on Tuesday.

       In October 2019, the 12-time ATP title winner had season-ending surgery on his right elbow. Last year, he tested positive for coronavirus and later suffered an injury to his shoulder while playing his second-round match at the French Open.

       The former world No. 4 has been on the comeback trail ever since. He won into the semifinals at the 500-level Citi Open in Washington last week, his first ATP final four since the spring of 2019.

       Nishikori's next scheduled tournament is the Aug. 14-22 Western & Southern Open in Cincinnati.

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