A medical examination in Barcelona this week will reveal the extent of Rafael Nadal's right knee injury.
The Spanish world No. 2 is confident he will be cleared of serious damage. Nadal, 23, said he was not concerned over his long-term future.
"No, I think (I'm) going to be OK," he said after retiring mid-match against No. 5 Andy Murray in the Australian Open quarterfinals on Tuesday night.
"I didn't have lot of problems for the last six months," Nadal said. "And today is the first time, no?"
Nadal looked to be in good physical form early in the match, running all over the court to track down Murray's blistering shots. But Nadal appeared to aggravate the knee early in the third set and was forced to retire while trailing 6-3, 7-6 (2), 3-0.
"We don't know the scope of the injury but there is something going on in there, something that wasn't there before,'' uncle and coach Toni Nadal told Spanish media from Australia. "Something felt wrong and it was the right decision to retire.''
Nadal is set to undergo MRI scans after arriving in Spain to determine the extent of the problem, with Toni Nadal quoted as saying that a preliminary ultrasound showed it "wasn't a serious problem.''
"You're always worried about these things, it's normal,'' Toni Nadal said. "It appears not to be what he had before and something else, but we must be prudent and wait and see.''
Nadal, one of the most amiable characters in tennis, bristled at suggestions he would have to further modify his training and playing style.
"Don't start, guys, with these questions right now," he said. "I think (this) is not the right moment. I think I changed the style to play. If you see my matches 2005 or 2004, 2006, I run a lot compared to now, no? So today I played against one of the best players of the world, and I think I wasn't run(ning) more than him.
"Remember, we are playing on hardcourts. Probably in this surface I have to play my best tennis, like today, if I really want to have chances to win."
Nadal's ranking will suffer significantly because of his failure to defend the Open title. But the Spaniard said he was satisfied over the quality of his form.
"I go out from this tournament very happy about my level because the perspective is much better right now than two or three months ago," Nadal said.
"When I lost in the (ATP World Tour finals in London) all the matches, I didn't see one way to play again my tennis. Now I am playing another time at my best level."
Nadal has not won a title since Rome in May. Murray next plays No. 14 Marin Cilic of Croatia in the semifinals.
The Associated Press contributed to this report.
