James Faulkner has been ruled out of the third Ashes Test with a fractured thumb, meaning Australia are sweating all the more on the fitness of Ryan Harris.
Harris has been struggling with a knee injury but did eventually work up to full pace today 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, who will play his 100th Test tomorrow, 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.''
Clarke prizes the opportunity to wrap up the Ashes 3-0 at the WACA far above the personal landmark.
"That's why it's most special for me - the fact that we have a chance to win the Ashes,” he said.
"With regards to being your 100th Test, it's not a focus for me at all. There's enough other reasons as to why this Test match is so special to me, and this team."
Clarke will be cheered on at the WACA by his nearest and dearest, and acknowledges his century will be memorable - whatever the outcome.
"It's fantastic that I've been able to play 99 Test matches for my country. It's something I'm certainly proud of. I'll have my family coming - which is extra special," he added.
He offered his congratulations too to Cook, three years his junior at 28, who will also win his 100th Test cap.
"He deserves a lot of credit for the success he's had over a long period of time for England,” Clarke said.
"He's a wonderful guy. I really enjoy playing against him. He's a very good captain, and I think he deserves all the credit he receives for playing 100 Test matches.
"He's always been a prize wicket for the Australian cricket team. His record speaks for itself."