Kei Nishikori provides "painful" injury update after withdrawing from multiple tournaments in Japan

Kei Nishikori has provided a "painful" injury update after being forced to withdraw from more tournaments on the ATP and Challenger Tours in Japan.

The former World No. 4 was absent for a year and a half before returning to the sport at the Challenger 75 Caribbean Open in Palmas del Mar, Puerto Rico. He saw great success upon his comeback, defeating Michael Zheng in the final to win the title.

After competing in several more Challenger tournaments, the 33-year-old returned to the ATP circuit at the Atlanta Open in July.

However, he was then dealt another blow after he sustained a knee injury that forced him to take more time away from the sport. After pulling out of the US Open, the Japanese player was hoping to come back to play the Japan Open as well as some Challenger tournaments in his home country, but has once again had to withdraw.

Nishikori recently took to social media to provide an update on his situation, detailing the "painful" emotional toll the withdrawals were taking on him.

"In June I came back for the first time in a while and played in a few events, started feeling better. Then my knee started getting worse, and here I am.

"I had to withdraw from all the event, the US Open that I was really looking forward to playing the Japan Open, and Challengers in Japan, that's really painful. This is a matter of my own body, I know I can't make an excuse, but still these days I feel like [saying to my body] 'Hey why couldn't you allow me to play matches, it's enough, it's about time'," he wrote in Japanese.

Despite this, Nishikori has also made it clear that he remains hopeful to be able to return as soon as possible.

"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 one day.

"These days I can't still move [freely on the court] but keep playing tennis, so I hope I'm almost there. 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.

"I'm sorry for those who looked forward to watching me playing Matsuyama and Kobe Challengers. I've not given up (playing in Japan), will try hard to play remaining two Challengers (Yokohama & Yokkaichi). If I can't play these tournaments, I'll try my best to be ready for the Australian Open.

"Believing all these days will help me to improve," he continued.