The in-form Australian has taken the cautious route to Wimbledon, deciding to pull out of his last-16 tie against Roberto Bautista Agut at the Mallorca Championship on Wednesday after suffering from abdominal pain.

The Australian, who's been a big hit with the local fans on the Spanish island, reckons he was sorry to have to disappoint them by withdrawing because of a painful abdomen muscle problem he'd suffered during Tuesday's win over Laslo Djere.

Taking doctor's advice, he played it safe, saying he wanted to take "no risks" with his best shot at Wimbledon in recent years just around the corner.

But the enigmatic Australian wasn't playing safe with his views about the ATP's plans to trial off-court coaching, saying that he believes the unique nature of the sport was being removed by the experiment.

The ATP will trial the system in the second half of the season, with players allowed to get instructions during qualifying and main draw matches in tournaments, including the US Open and the ATP Finals.

Patrick Mouratoglou, who helped guide Serena Williams to glory, congratulated the ATP for "legalising a practice that has been going on at almost every match for decades" but Kyrgios was adamant in his opposition.

"Completely disagree. Loses one of the only unique traits that no other sport had," Kyrgios responed on Twitter.

"The player had to figure out things on his own. That was the beauty of it. What happens if a high profile player versus a low ranked player who doesn't have or (cannot) afford a coach?"

Mouratoglou was involved in the most high-profile piece of off-court coaching at the 2018 US Open final when Williams was given a warning for his gesturing.

The new trial is due to begin on July 11, the day after the end of Wimbledon, where Kyrgios has good reason to believe he could have his best run yet after reaching two grass-court semi-finals in the space of two weeks in Stuttgart and Halle.

"I'm really sorry I'm going to have to withdraw from tonight's match here in Mallorca. I have been playing a lot of great matches lately and unfortunately I woke up with a pain in my abs," Kyrgios said in a statement released by the organisers on Wednesday.

"I went to see the tournament doctor right away and he advised that I don't play tonight. I really value the Mallorca Championships but I will follow his advice as I don't want to risk Wimbledon next week.

"I was really looking forward to tonight's match as I've been loving my time here. Mallorca is such a beautiful island with really nice people."

Javier Cerrato, the tournament doctor, reported: "Nick Kyrgios suffers pain in the rectus abdominis on the left side due to the accumulation of matches in recent weeks and the effort of yesterday's first round match.

"This will not allow him to return to the court tonight."

Organisers must have been left disappointed that his exit also prevented the prospect of a blockbuster quarter-final for the Australian against world No.1 Daniil Medvedev, who earned his place in the last-eight on Wednesday with a 4-6 6-3 6-2 win over Aslan Karatsev.

Australian Associated Press