"It all depends on my body that doesn't seem to be getting better" - Kei Nishikori addresses injury concerns after failed comeback

Kei Nishikori continues to struggle with injuries in his pursuit of a comeback to competition. He made a brief return to the Tour earlier this year, but was again sidelined because of a recurrent knee issue ahead of the US Open.

Nishikori lifted a challenger crown in June before making the quarters at Atlanta, only to be forced to withdraw from the Citi Open and Flushing Meadows. He has not played since.

Taking on social media to share an injury update on Wednesday, Nishikori said he was looking forward to playing at the US Open. He, however, was quick to add that his body did not seem to be getting better before announcing his decision to withdraw from some of the upcoming Challenger events.

"In June I came back for the first time in a while and played in a few events, started feeling better," Kei Nishikori wrote. "Then my knee has started getting worse, and here I am. I had to withdraw from all the event, the USO that I was really looking forward to playing."

"It all depends on my body that doesn't seem to be getting better, I'm gonna put up with it and work hard a little bit more," he continued. "I'm sorry for those who looked forward to watching me playing Matsuyama and Kobe Challengers."

Nishikori further described the "painful" experience of being forced to battle against his own body, saying he continues to put in the work needed for him to get better.

"Japan Open, and Challengers in Japan, that's really painful," Kei Nishikori wrote. "This is the matter of my own body, I know I can't make an excuse, but still these days I feel like 'hey why couldn't you allow me to play matches, it's enough, it's about time'."

"What I have to do remains the same, I go to the gym on a daily basis telling myself that I'm gonna be fine someday," he continued. "These days I can't still move (freely on the court) but keep playing tennis, so I hope I'm almost there."

Kei Nishikori hopeful of Australian Open return

Despite the repeated setbacks, Kei Nishikori has not ruled out playing at the two remaining Challengers events in Japan — Yokohama and Yokkaichi.

The Japanese said that he will try hard to regain full fitness and play in front of home fans. He further added that if he fails to make it to these tournaments, the comeback would likely be pushed to the Australian Open next year.

"I've not given up (playing in Japan), will try hard to play remaining two Challengers (Yokohama & Yokkaichi)," Kei Nishikori said. "If I can't play these tournaments, I'll try my best to be ready for the AO. Believing all these days will help me to improve"

Nishikori peaked at a career-high world ranking of No. 4 in March 2015. He has reached one Grand Slam final, the 2014 US Open, where he came up short against Marin Cilic.