The 34-year-old, who featured in his side's opening defeats to Chile and the Netherlands, is currently struggling with a back problem.
"It's not looking too good," he told FIFA.com. "I'm very disappointed. Leading up to the World Cup, I was struggling with my back and we've done everything possible to get it right.
"The medical staff have been brilliant and got me back on my feet, but when you have injuries, other problems start arising and it's hard to carry through the games."
Both the Aussies and Spain are unable to reach the second round of the tournament after losing their opening two matches.