Kokkinakis, who in 2015 reached a career-high world No.69 ranking, says he was depressed during his stint away from the sport, so much so he avoided the spotlight as he struggled to leave the house.

"But I just got hurt all the time and couldn't make the most of momentum I built. It was horrendous. It was probably as low as any tennis player could feel."

"The frustration has killed me. The toughest thing is how much I've missed tennis the past four years with all the injuries I've had. A lot of the guys I grew up beating and being above – seeing them do so well and move past me – I thought I was there with these players.

"I didn't want to go out while I was injured because I didn't feel like I deserved it," Kokkinakis said.

"That's just how I am. I feel if I have a good tournament, go on a good run or play a lot of matches, I feel like I'm deserving of going out and having a good time. I felt like I didn't need it or deserve it. If I went out I knew I would have a bunch of people asking me how the shoulder was and when I'm back. I have a really tough time lying to people when they ask me how I'm feeling. If everything was pretty average, I could have said I was close. But the tough part was that inside I was pissed off so I would rather avoid it.

"I reckon I got depressed. But I think that's normal for anyone when what you do and what your life revolves around gets taken away. You don't know what to do. I was trying to plan my days and spread things out so I would take up a chunk of the day. I really struggled to occupy my time. It was pretty shit to be honest."

Shoulder surgery in October 2015 was only meant to sideline him for two to three months, however complications saw him wait 10 months before his first competitive match at the Rio Olympics.

With his comeback story looking like reaching a happy ending, Kokkinakis lost seven kilograms in a few days while fighting a stomach bug before tearing his pectoral muscle at practice leading into the US Open.