"It's heartbreaking, but I'll be here next year" - Kyrgios on withdrawing from his Japan Open quarterfinal match

Aussie tennis star Nick Kyrgios was left heartbroken after a left-knee injury forced him to pull out of the Rakuten Japan Open ahead of his quarter-final showdown with Taylor Fritz on Friday night.

"It's obviously very disappointing," the Australian said in a somber press conference. "It's one of my favorite tournaments. I've had great memories here... It's heartbreaking, but I'll be here next year. That's for sure."

The Tokyo fifth seed also pulled out of Atlanta earlier this year with a left-knee issue before rebounding to reach the US Open quarter-finals.

"I've been playing amazing tennis all year and actually was dealing with a bit of a knee issue around the US Open time," Kyrgios explained. "I got back home and probably didn't take enough time off, to be honest. I went straight back into training."

The 2016 Tokyo champion had been in fine form this week with singles wins against Chun-Hsin Tseng and Kamil Majchrzak in addition to a run to the doubles semi-finals alongside Thanasi Kokkinakis.

"The Japanese fans are some of my favorite to play in front of," Kyrgios said. "It's been such an amazing week. Obviously playing four matches and winning all four, I've been feeling great. I definitely felt like I was a threat to win the tournament and go all the way in singles and doubles.

"When your body lets you down, it's not a good feeling. I know in this case it's probably overloading rather than not being fit enough. I think t's almost being too excited to get on the court and maybe training a little bit too much. So it's positive, but heartbreaking at the same time."

Kyrgios plans to return to the ATP Tour later this month in Basel and Paris.