Just a sad day for an injured Rafael Nadal at the Australian Open

— -- MELBOURNE, Australia -- One of the fittest athletes in tennis, Rafael Nadal struggled to walk as he entered the media room at the Australian Open following his loss in the quarterfinals Tuesday night. He stepped gingerly onto the two stairs that led to the table where he would answer questions. Nadal grimaced in pain as he lowered his body to sit. It was difficult to watch.

Only 30 minutes earlier, the crowd at Rod Laver Arena was waiting in anticipation for the start of the fifth set between Nadal, the top-seed here in Australia, and Marin Cilic, the No. 6 player in the world. The high-quality play between the two, at that point, was worthy of a championship match.

And just like that, it was over.

After Cilic broke Nadal to give him a 2-0 lead in the final frame, the Croatian pumped his hand in celebration not realizing what was going on. Then he caught a glimpse of Nadal approaching the chair umpire, signaling a sudden and unexpected retirement to seal a 6-3, 3-6, 7-6 (5), 6-2, 2-0 win.

What a shame. Nadal was making a bid to become the first men's player in the Open era to win each of the Grand Slam events twice. And he was making his run in a tournament that's featured huge upsets in both the men's and women's field.

Needless to say, the Nadal- Roger Federer rematch from a year ago is not happening. Instead, Nadal's immediate future will be an MRI on Wednesday to figure out the extent of an injury that he indicated was in his upper right leg.

With his unexpected departure, Nadal took a parting shot at tennis officials in the final question of the Q&A with the media after being forced to retire from a Grand Slam event for just the second time of his career.

"Somebody who is running the tour should think a little bit about what's going on," Nadal said. "Too many people are getting injured. If we keep playing on this very, very hard surfaces what's going to happen in the future with our lives."

It's been a week in which Nadal has had several complaints. Last week, his targets were the heat (he claimed it was too dangerous in the midst the two-day heat wave on Thursday and Friday) and the preferential treatment some players received to avoid playing in extreme conditions.

Both justifiable concerns.

Before Tuesday, Nadal never mentioned any kind of health concerns over the first four rounds, which seemed to be encouraging news. He ended last year early with a knee injury and decided to skip the Australian Open tune-up events in Brisbane and Sydney.

Nadal, whose only Australian Open win came in 2009, appeared primed to make a return trip to the finals. He had dropped just one set all week. And he was playing a semifinal opponent in Cilic whom he had beaten five of the six times they had played.

Cilic's only career win against Nadal came in 2009, at a time when the current defending US Open and French Open champion was recovering from knee and abdominal ailments.

In a match that was competitive early Wednesday (Nadal won an exciting third-set tiebreaker to take a 2-1 set lead), the world No. 1 said he started to feel pain in the next frame. He took a medical break in the fifth game of that set and said he had limited his mobility the rest of the match.

It wasn't long afterward that Nadal approached the chair umpire and shook his hand. It stunned nearly everyone in the arena, most of whom probably never saw the gesture.

"It's very unfortunate because Rafa is always fighting hard, always gives his best on the court," Cilic said. "He played a good tournament. Obviously, it's very sad for him to finish the way he did."

Sad for Nadal but an amazing opportunity for Cilic on a day in which the No. 3 seed, Grigor Dimitrov, was upset by Kyle Edmund of Great Britain. Cilic will play Edmund in a semifinal Thursday.

Cilic, in beating a world No. 1 for the second time in his career, reached his fifth Grand Slam semifinal. And in this upset-filled tournament where the remaining players in the men's field feature Roger Federer and a bunch of other guys who don't really scare you (Edmund, Tennys Sandgren, Hyeon Chung and Tomas Berdych), Cilic has to like his chances.

"For me a big focus is to continue with my own game," Cilic said of playing Edmund. "Hopefully I'm going to have another great match."

As for Nadal, who knows what's next. After shaking hands with Cilic, he walked over to his bench and slammed one of his wrist bands to the ground, a sign of the disgust he felt in being forced to retire.

Later, in the interview room, Nadal couldn't really pinpoint what happened to this body.

He came in to tournament looking fit and trim. His massive and well-defined arms were on full display as he wore a sleeveless shirt throughout the tournament.

He got through his first four matches in a relative breeze. But it all came to an end abruptly, a sudden departure for a guy who would normally have to be carried off the court.

"I worked hard to be here," Nadal said. "We did all the things that we believed were the right things to do to be ready."