It never rains but it pours - that must be the feeling in the Australian dressing room as Simon Katich struggles to be fit for the third Ashes Test.

Katich suffered a recurrence of an Achilles injury on day three of the second Test in Adelaide, but opted to open the innings on Monday despite being in pain. He batted for 108 minutes and contributed 43 to Australia's 238 for four - 137 runs behind England's first innings of 620 for five declared.

The left-hander went to the hospital straight after his dismissal, but the results of the scans will only be known on Tuesday.

Team-mate Michael Hussey, though, fears the worst.

"Kato is obviously pretty sore... it doesn't look too good," Hussey is quoted by AAP.

"It was an inspirational performance really.

"Even in the field, I was trying to get him to go to gully and he wouldn't have a bar of that... we were trying to get him in the slips and he wouldn't get in the slips.

"His stubbornness is probably a big characteristic of him.

"He's willing to show that he will fight all the way, even though he's on one leg.

"Even the way he played today, I thought he played really well considering he was obviously in a lot of pain."

Hussey, who was 44 not out at stumps on day four, offered to open the innings with Shane Watson, but Katich was having none of it.

"Kato wouldn't have a bar of that either, he said 'I'll make sure I'm there, it's my job, I have got to do it'," Hussey said.

"I have known Kato for a long time and you don't expect anything less."