MELBOURNE, Australia -- A despondent Rafael Nadal dipped his head and appeared to fight back tears as he sat courtside on Rod Laver Arena, trailing American Mackenzie McDonald 4-6, 4-5 in the second round of the Australian Open. His eyes locked with wife Xisca, who was having no luck hiding her emotion in the players' box.

Nadal stood before trudging off court and back through the tunnel to undergo an injury timeout.

Moments earlier, the Spaniard had pulled up in pain when chasing a ball at the back of the court. He winced in agony and promptly dropped to his knees after appearing to injure his hip. It looked like he was finished.

Nadal received a raucous applause when he returned to the court, and the decibels rose even higher once he reached for his racket and headed to the far baseline, readying himself to play on.

McDonald promptly wrapped up the second set to double his advantage, but a clearly hampered Nadal was going to make his opponent work for this victory. Nadal was hurting, physically and emotionally, but refused to throw in the towel -- something that just doesn't appear to be in his DNA.

Despite a gutsy third set from Nadal, it was McDonald who again came out on top, securing the match 6-4, 6-4, 7-5. The reigning men's champion had been knocked out of the draw, but his fight and determination endeared himself to all.

"To be the defending champion here, I didn't want to leave the court with a retirement," Nadal later said. "I tried until the end. I was not able to hit the backhand at all. I was not able to run for the ball. [Winning] was not possible, but I just wanted to finish the match.

"Try your best to the end. That's the philosophy of the sport. I tried to follow that during my tennis career."

Nadal will undergo scans in the coming days to determine the extent of his injury before committing to any upcoming tournaments.

"I have history in the hip, [but] I don't know if it's a muscle, if it's the joint, if it's the cartilage," he said. "Hopefully it's nothing too bad. I really hope that it doesn't put me out of the court for a long time, because then it's tough to make all the recovery again. I went through this process too many times in my career. It's not only the recovery, it's all the amount of work that you need to put together to come back at a decent level."

Nadal's injury setback is the latest chapter in what has been a year of two halves for the 22-time Grand Slam champion.

He experienced the ultimate highs of winning both the Australian Open and French Open in the beginning of 2022 -- moving him ahead of Novak Djokovic in the race for the most major wins in men's tennis -- before suffering an abdominal tear at Wimbledon, which forced him to withdraw from his semifinal match. Nadal then reached the fourth round at the US Open before his form completely abandoned him.

Nadal arrived at Melbourne Park with just one win from his past six matches and in the midst of perhaps the greatest slump of his illustrious career.

During the lean patch, Nadal suffered defeats to Tommy Paul at the Paris Masters, as well as against fellow top 10-ranked players Taylor Fritz and Felix Auger-Aliassime at the season-ending ATP Finals. He then began 2023 by falling to Alex de Minaur and Cameron Norrie at the United Cup in Sydney.

"It's true that I have been losing more than usual," Nadal said ahead of the tournament. "I think I am humble enough to accept that situation. I need to build again all this momentum. I need to build again this confidence with myself."

Nadal's first-round win over Britain's Jack Draper at Melbourne Park might have halted his losing streak, but it did little to instill confidence that he was back to anything even remotely close to his devastating best.

He racked up an unusually high amount of unforced errors, struggled with his serve and even looked nervous for large periods. His trademark whippy forehand consistently let him down, and on several occasions he struck routine smashes into the net.

It was a theme that continued against McDonald. Nadal appeared utterly dumbfounded with how he was playing. He frequently shook his head in disbelief, and at times looked to the heavens, as though he sought an answer as to why his form had completely tailed off.

But even on Wednesday, after a match that must have frustrated him to his core, he vowed he will continue.

"It's very simple: I like what I do," he said in the news conference after the match. "I like playing tennis and I know it's not forever. I like to feel myself competitive. I like to fight for the things that I have been fighting for almost half of my life.

"When you like do one thing, at the end, sacrifices always make sense, because the "sacrifice" word is not like this. When you do things that you like to do, at the end of the day, it's not a sacrifice. You are doing the things that you want to do."