Nick Kyrgios withdrew from the Japan Open just minutes before his quarter-final on Friday with a sore left knee, calling it "heartbreaking".
The mercurial Australian star had been scheduled to play third-seeded American Taylor Fritz, who will now play Canada's Denis Shapovalov, seeded seventh, in the last four on Saturday.
At a hastily announced press conference when the match was due to begin, world number 20 Kyrgios said he had "been playing amazing tennis all year" but it had been physically taxing. "I actually was dealing with a bit of a knee issue around the US Open time, and got back home, probably didn't take enough time off, to be honest.
I went straight back into training," said the 27-year-old. "It's heartbreaking. When the body lets you down, it's not a good feeling." Kyrgios will now head home, but said he still plans to play several events in the run-up to the Australian Open in January, and promised to return to the Japanese tournament in 2023.