Andy Roddick spoke of his frustration after a hamstring injury forced him to retire from his Australian Open second-round clash on Thursday.
The American 15th seed battled with the problem but eventually pulled out of his clash against local Lleyton Hewitt while trailing 3-6 6-3 6-4.
Roddick, 29, said any explosive movement was causing him pain, and added he was struggling to cope with injury problems.
"It's frustrating. It's discouraging. You know, your sensible mind says to have a sense of perspective - you still have it pretty good," Roddick said afterwards.
"The competitor in you feels terrible and wants to break stuff. I can't really complain. I had 10 years pretty much of a clean slate. That's a lot more than most people get."
"The last, you know, two years has been pretty tough. It's tough physically. It's as tough mentally, though. It's hard."
Roddick's retirement handed Hewitt a passage into the third round, where he will meet highly-rated Canadian Milos Raonic.
The 2003 US Open champion will also miss the United States' Davis Cup meeting with Switzerland, one he said he was unlikely to play in anyway.
Meanwhile, Hewitt was pleased with the way he responded to playing against an injured Roddick.
"Mentally, it was one of my better performances tonight throughout my career," the Australian said.
"To keep your mind ticking over the whole time isn't easy. It would have been a lot easier if you weren't playing a big server, he could keep holding his serve out there because there was obviously nothing wrong with his shoulder."
"That was hard. That's probably the biggest positive to take out of tonight."