Australia captain Michael Clarke is hoping seamer Ryan Harris will be fit for the third Ashes Test in Perth after his possible replacement James Faulkner was ruled out with a fractured thumb.

Former Lowerhouse professional Harris has been struggling with a knee injury but did eventually work up to full pace on Thursday after a slow start to the net session.

If he was ruled out, Australia would not be able to call on Faulkner, who was 12th man in Brisbane and Adelaide, matches the home side won to establish a 2-0 series lead over England with three games to play.

"James was struck on the right thumb while batting in the nets and was subsequently taken for an x-ray which revealed a fracture of the thumb," said Australian team doctor Peter Brukner.

"As a result he will not be available for the third Test. His progress will be monitored for a return to playing duty depending on how quickly the injury heals."

Although Faulkner has found chances at Test level hard to come by, he is a key member of Australia's limited-overs side and was expected to feature heavily in the one-day series and T20 internationals which follow the Ashes.

His absence means Australia will look to either Doug Bollinger or Nathan Coulter-Nile should Harris not make it.

Captain Michael Clarke said: "I hope everyone will come up.

"There is the obvious one, 'Rhino' bowled today, so we are going to wait and see how he pulls up.

"But I am confident he will be fine."