MELBOURNE, Australia -- Rafael Nadal limped off the court after quitting in pain early in the fifth set on Tuesday to send Marin Cilic into the semifinals of the Australian Open, 3-6, 6-3, 6-7 (5-7), 6-2, 2-0.
The Spanish top seed, who had been treated on his upper right leg in the fourth set, pulled the plug after almost four hours of intense battle with the sixth seed and 2017 Wimbledon finalist.
Nadal came to Melbourne with a huge question mark hanging over his right knee as he started his season late.
"Tough moments," Nadal said. "It's not the first time an opportunity is gone for me. I'm a positive person, and I can be positive, but today is an opportunity lost to be in the semifinals of a Grand Slam and fight for an important title."
The 31-year-old failed to finish a match for only the third time in almost nine years, with one of his pullouts coming in Melbourne, 2010, in a quarterfinal against Andy Murray.
"It's difficult to know exactly what it is now. It's difficult to know exactly the muscle. It just happened minutes ago, Nadal said. "We need to wait a couple of hours. Tomorrow I am going to do a test, an MRI here, then we will know."
Cilic faces a semi with unfancied Briton Kyle Edmund, who stunned third seed Grigor Dimitrov, 6-4, 3-6, 6-3, 6-4.
Nadal was struggling to walk normally as he left the court, after quitting as he lost the second game of the fifth set despite saving five break points before being caught by a Cilic pass.
"It was an unbelievable performance from both of us," Cilic said. "It was uncomfortable for Rafa, but he's a competitor who always gives his best.
"It was sad to see him finish like this. I had to continue with my own game and not look too much across the net."