MELBOURNE, Australia — Defending champion Rafael Nadal retired from his quarterfinal against Andy Murray with an injured knee, then predicted the Scottish player would end his Grand Slam title drought by winning the Australian Open.

"For Andy, I think he deserves to win his first Grand Slam. And I think he's going to do it," Nadal said after a right knee injury forced him to concede Tuesday's quarterfinal while trailing 6-3, 7-6 (2), 3-0.

"There's a very good chance for him. First thing, he's playing very well," Nadal said. "Second thing, he's already in the semifinals. He's only two matches away."

Andy Roddick also went out of the Australian Open on Tuesday, struggling with a shoulder injury before going down in five sets to Marin Cilic.

Nadal said he didn't want to risk more damage by playing and potentially having to spend long periods off the tour with knee tendinitis.

"Similar thing that I had last year," Nadal said of the pain. "It was impossible to win the match."

Murray will play a semifinal against Cilic, who beat No. 7 Roddick 7-6 (4), 6-3, 3-6, 2-6, 6-3 earlier Tuesday.

Nadal struggled with knee tendinitis and was unable to defend his Wimbledon title last season after beating Roger Federer in the Australian Open final. He received on-court treatment from a trainer for his knee after losing the second set.

Three games later, the Spaniard decided he couldn't keep playing.

"I didn't know when he hurt his knee, when he started feeling it, but from my side, I played very well," said Murray, who is hoping to end a seven-decade British drought at the majors. "I deserved to be up when the match stopped."

The 22-year-old Scot can hardly wait to play his semifinal against Cilic.

"I lost to him at the U.S. Open in straight sets, so I'm looking for a little revenge," Murray said. "If I play like I did tonight, I have got a good chance. Obviously, nerves are going to be there with an opportunity to make a final of a Slam."

Murray's only Grand Slam final appearance ended in a loss to Federer at the 2008 U.S. Open.

Roddick struggled through a right shoulder injury that impaired his movement, but he expects no long-term damage.

Still in the equation at Melbourne Park is three-time champion Federer, who plays Nikolay Davydenko in the quarterfinals on Wednesday. Novak Djokovic, the 2008 champion, takes on the same year's runner-up Jo-Wilfried Tsonga in the other quarterfinal.

Roddick's only major has been the 2003 U.S. Open, the last time an American man has won a Grand Slam singles title, marking the country's longest drought in men's majors.

Despite playing strongly in the third and fourth sets to level the match, Roddick fell apart in the final set, allowing No. 14 Cilic to break twice and send the last American man out of the singles draw at Melbourne Park.

Roddick said he didn't practice Monday after feeling a twinge in his shoulder during Sunday's fourth-round win over Fernando Gonzalez.

"The trainer said it was stemming from the neck down," Roddick said. "By the end of the first set, I was pretty numb in the bottom two fingers. I could still hit it pretty hard; I was just having trouble controlling it."

Seven-time Grand Slam singles winner Justine Henin hasn't won a major in two years — because she hasn't played in one. Henin, who returned from 20 months in retirement, advanced by beating Nadia Petrova 7-6 (3), 7-5 to take out the last seeded player in her half of the draw.

Henin, unranked and playing on a wild-card entry at Melbourne Park, will face Wimbledon semifinalist Zheng Jie, who beat Russia's Maria Kirilenko 6-1, 6-3 to equal her Chinese record for the best run at a major.

"I just went for it with my heart. Finally I could make it, and I'm very happy," Henin said. "At the end I played much more aggressive tennis."

Henin ended a highly successful run in Melbourne for Petrova, who ousted two reigning major champions: U.S. Open champion Kim Clijsters in the third round; and French Open champion Svetlana Kuznetsova in the fourth.

Kirilenko had taken out big names in her section, too, starting with 2008 champion Maria Sharapova in her first round and her fourth-round victory against last year's finalist Dinara Safina, who retired with a back problem.

Henin retired in May 2008 while holding the No. 1 ranking and had not played at a major since losing in the quarterfinals to Sharapova here that season. Henin won the 2004 Australian title and reached the final in 2006.

The loss to Sharapova confirmed to Henin that she needed a break. Now she's feeling as good as ever.

Roddick, who took two months off at the end of last year because of a knee injury, was also positive after his loss.

"All signs at this point are good," Roddick said. "Whether it was a nerve that was compressed or something, I don't know, cutting off something. But they don't think it's going to be anything too serious long-term. I'm sure we'll take the proper precautions and check it out."