Nick Kyrgios courted controversy once again at the Shanghai Masters on Tuesday, retiring midway through his match with Steve Johnson for seemingly no reason.

The Australian enjoyed a run to the China Open final last week, only to be outclassed by Rafael Nadal after appearing to be negatively affected by a line call going against him in the opening game.

In the wake of that defeat, Kyrgios revealed that his charitable foundation to help disadvantaged and underprivileged children has given him a fresh focus to motivate himself.

But there was little sign of the 22-year-old turning over a new leaf as he shook hands with Johnson and promptly walked off court after losing the first set on a tie-break.

Kyrgios felt his right shoulder in his opening service game but seemed unhurt thereafter and took a 3-0 lead in the breaker despite complaining about how tired he was, having played in the doubles with Lucas Pouille a day earlier.

At 4-2 up, Kyrgios refused medical help at the change of end and was then hit with a point penalty for an audible profanity and could be heard to say that if he lost the breaker he would retire from the match.

Johnson's thumping ace down the middle saw the American prevail and Kyrgios stuck to his word.

The incident comes a year after Kyrgios was suspended for eight tournament weeks and fined by the ATP after 'tanking' in a match against Mischa Zverev at the same event.