Kunieda has won 28 Grand Slam singles titles and four Paralympic gold medals, and is the most successful men's wheelchair tennis player of all time.

The 38-year-old also has two Paralympic bronze medals in men’s doubles.

Last year, he won the Wimbledon to complete the career Grand Slam.

"I topped the year-end rankings for the 10th time last year, so I have concluded that I have done enough," Kunieda said.

"I kept thinking about retiring after my dream came true at the Tokyo Paralympics.

"I began to feel I didn't have much energy left to play on the tour when I won the long-sought Wimbledon title last year."

He also has 22 Grand Slam doubles titles to his name.

Kunieda turned professional in 2009.

"Please forgive me for retiring while being No. 1 in the world," said Kunieda, according to Kyodo News.

"Tough competition allowed me to get this far."

The International Tennis Federations states that the Japanese national has been spent 582 weeks as the men's wheelchair singles world number one during his career.