[Editor's note: This story was originally posted before Andy Murray's announcement Friday that he plans to retire and is targeting this year's Wimbledon as the final tournament of his career.]

Andy Murray bit back the tears. As his voice faltered, this public display of emotion was not at the lectern following a Grand Slam final, but instead during an on-court interview just after the opening round of this year's Brisbane Open.

If you wanted any sign of how hard this man has pushed himself in the past couple of years to right his troublesome hip injury, and how he has shouldered the mental strain, then his on-court reaction to his victory against James Duckworth on New Year's Day said it all.

"It's been a hard 18 months, with a lot of ups and downs," Murray said during the interview. "It's been tricky to get back on the court and competing again. I'm happy I'm back out here again. I want to enjoy as much as I can and enjoy playing tennis as much as I can as I don't know how much longer it's going to last."

Andy Murray is not sure what to expect from himself heading into the Australian Open. SAEED KHAN/AFP/Getty Images

It was just his seventh win since his quarterfinal loss at Wimbledon in 2017. The past year had mentally taken its toll. As the frustration mounted and the time away from the court increased, he recognized his own sporting mortality.

Murray's final act of 2018 was to draw a line through the most frustrating of years via his Instagram page. Next to a photograph where he was swigging a bottle of champagne with an array of nicely chilled beverages lined up in front of him, he wrote: "Celebrating the end of 2018. What a s--- year that was!"

It was Murray, 31, at his blunt best.

And on Friday, just days before the start of the 2019 Australian Open, Murray drew another line - a plan to retire this year because "I can't keep doing this ... I need to have an end point, because I was just playing with no idea when the pain was going to stop."

Last year saw him undergo hip surgery in January, opt out of the French Open, withdraw from Wimbledon and then exit the US Open in the second round. He played just six tournaments. Entering this season, there have been doubts over whether he will ever be able to regain the form and fitness that led him to three Grand Slam titles.

But though Murray had a forgettable year, there was some inspiration. Reigning men's No. 1 Novak Djokovic started last season in relative obscurity as he tried to come back from an elbow injury, while the residue of some unflattering public-life stories lingered on.Amazingly, Djokovic won back-to-back Slam titles, at Wimbledon and the US Open, and climbed back atop the tennis tree. He had been written off in some corners but trusted in his own ability, which eventually shone through.

Djokovic said one of the challenges of coming back from a nagging injury is about fighting your own doubts.

"I understand one of the biggest struggles [Murray] is going through, and I personally had in my experience with the elbow is: Who to trust?" Djokovic told the media at the ATP World Finals. "At the same time you feel a certain way or procedure that has been determined for you in your recovery is not the most appropriate one, that your gut feeling is telling you something else. Then you change the direction and that loses a lot of time.

"You have to make up that time and then you get emotionally disturbed because you're wasting time, not playing on the tour, 31 years old and all these thoughts are going through your mind."

But there are then the memories of glories past that can plague a man accustomed to winning, as Roger Federer found.

"The problem is that he has been world No. 1, [Murray] has won double Olympic gold, he has done it all," Federer said in London. "It's not enough to play last 16 or quarters. For that I feel he'll probably want to feel like he can play top-10 level, then top five, you know how it is. It's going to be interesting to see how he's going to come back. But I'm confident that if he does feel 100 percent, it's not going to be a problem for him to play at the very top."

A hip injury forced Andy Murray to miss a good amount of the 2018 tennis season. Julian Finney/Getty Images

While Federer, Djokovic and Rafael Nadal have trimmed the Big Four to three in Murray's absence, the two-time Olympic gold-medal winner has continued to watch on with unrelenting competitiveness. "It's killing me not to be able to get out there competing with them," Murray said in Brisbane.

The Australian Open offers him a chance, but he will have to balance on the tightrope of frustration and pain management at a tournament where he is a five-time runner-up.

Murray oscillates between emotions, leaving everything out on the court, locked in this bubble of self-criticism but overflowing with self-belief. There are no gray areas in his on-court persona.

Despite his inactivity, Murray has stayed in the public eye with his Instagram posts. He has acknowledged his frustration while maintaining a duty to keep his avid supporters up to date, which gently nurses the hope they will one day see him collect another Slam.

Amid the fitness updates, ice baths, a tennis-playing snowman, an encounter with Wayne Rooney and some snarky posts around the (wrong) perception he is "boring, miserable" and has "no personality," there was one photograph of him as a child.

This was a year ago. As he wrote, "I choose this pic as the little kid inside me just wants to play tennis and compete. I genuinely miss it so much and I would give anything to be back out there. I didn't realise until these last few months just how much I love this game. Every time I wake up from sleeping or napping, I hope that it's better and it's quite demoralising when you get on the court it's not at the level you need it to be to compete at this level."

Here was the reluctant hero, the man now missing his hobby and profession, hoping he would get back to the standard he was before.

Andy Murray, a five-time runner-up in Australia, pulled out of last year's event. EPA/GLENN HUNT

He posted a photograph on Instagram of him next to the Australian Open trophy, saying: "The closest I'll ever get to the Aussie Open trophy [laugh/cry emoji] #5timeloser."

He followed it up by dispatching a troll who had accused him of only being motivated by money. One watch of the Brisbane interview was enough to dispel such a nonsense suggestion, but even though he has been in the shadows, the slightest glimpse of spotlight brings renewed intrigue and hype.

One day, Murray's 2018 campaign will be looked on as a defining year -- either one in which his time away from the sport gave him a new lease of life or one in which Old Father Time started his merciless stranglehold on the career of a once in a century British sportsman.

Murray's return to tennis begins in earnest in a few days at the Australian Open, where he will use his protected ranking to enter the field. His hip is still an issue. His Friday press conference tells the world he has his limits.

Whatever setbacks he's had, Murray still remains the rarest of sports stars. He made the improbable possible by offering British tennis a champion, when for so long hopes and dreams proved futile.

Seems as though regaining his movement in the sport he loves is, by comparison, a small step to take.