Rafael Nadal, Andy Murray and Stan Wawrinka are prepared to challenge No. 1 Novak Djokovic and Roger Federer in 2019. But even if their ambitions aren't compromised, their bodies certainly are.

All three stars dealt with significant injuries that curtailed their playing time and effectiveness in 2018. Nadal, ranked No. 1 for most of the year, hit spectacular high notes, but his year was compressed between ominous bookends when he retired in the late stages of both the Australian and US Opens.

The return of half of the Big Four and a replenished Wawrinka should be cause for celebration. But so far, eager fans have had to settle for sober injury updates and cautiously articulated hopes.

Rafael Nadal and Andy Murray are hoping to feel physically better by the time the Australian Open begins. AP Photo/Lionel Cironneau

"I started about two weeks ago and I am taking small steps forward," Nadal told reporters at the Mubadala World Tennis Championships, an exhibition in Abu Dhabi, a few days ago. "I am just making sure I am moving forward and it's not a step backward. I know I have time to be ready for Melbourne at 100 percent."

Nadal lost to Kevin Anderson in his Abu Dhabi debut and then pulled out of the third-place match.

"I want to do things step by step," he said. "I spent more time on court than I thought."

The loss means little on the face of it, but the match lasted under two hours, hardly the sort of taxing battle he could face in Melbourne. Nadal, a prudent man at the best of times, might be erring on the side of caution. Then again, perhaps his age (32) and the punishing style he has pursued as a pro for a decade and a half are catching up. He's starting to look like a hard-worked, high-mileage pickup truck. No sooner is one thing fixed than another breaks down.

Melbourne has never been very kind to Nadal, a pattern that started long before Federer ambushed him in the fifth set of that amazing final at the start of 2017. The Australian Open has been Nadal's least productive major (1-3 in finals), even though he played some of his most memorable matches there. Nadal also was forced to retire twice in the late going.

A year after Nadal narrowly lost the 2012 final to Novak Djokovic (in a storied match that fell just seven minutes short of six hours), Nadal was back in the championship match, poised to make the Grand Slam singles title derby a real race with Federer. But Nadal's back locked up. As a result, Wawrinka easily won his first major, Federer soon added distance to his lead in the race for major titles and Nadal's injury woes only increased.

Murray -- or Sir Andrew Barron Murray, OBE, if you prefer -- could have even more to worry about than Nadal because of the nature of his injury. Any hopes Murray had for full, relatively quick recovery from hip surgery were quickly dashed last summer, and he may not have made much progress since.

"I still have some pain in my hip but I need to play matches and see how it feels when I am able to play three, four, five matches in a row and take it from there," Murray told reporters as he prepared to make his 2019 debut in Brisbane. "I would just like to get through the tournaments and feel like I am able to compete and not be restricted by my hip."

Murray was reluctant to go under the knife last January, knowing full well that hip problems can be career-threatening and require lengthy rehab. Murray's fears were reflected in the Instagram message he posted once he made his decision: "Surgery is also an option, but the chances of a successful outcome are not as high as I would like, which has made this my secondary option, and my hope has been to avoid that."

Murray, 31, began his comeback in 2018 in mid-June at Queens Club. He ended up pulling the plug on his year in late September, finishing a disappointing 7-5 for 2018. His ranking is down to No. 256.

Wawrinka, starting the year ranked No. 66, had left knee surgery in the late summer of 2017, but his comeback in 2018 was halting and marred by continuing knee issues. "I wanted to just play a few tournaments to test the knee," Wawrinka said following his return from a three-month layoff in mid-May. "But I knew that I needed a lot of time to work on my fitness."

The ideal degree of fitness proved difficult to attain for a burly 33-year-old who was not known at the best of times for his movement or speed. Wawrinka's results fluctuated wildly in mid-2018 and, like Nadal, he terminated his campaign prematurely. He pulled out of Basel with a bad back.

The tuneup events for the Australian Open in the coming days will tell us a lot more about the chances of these three Grand Slam champions. We could use some good news.