Australia captain Pat Cummins cast doubt on Nathan Lyon's ability to recover in time for the fourth Ashes test in Melbourne after his side celebrated retaining the urn with two matches to spare against England in Adelaide on Sunday.
The spinner injured his right hamstring on the final day of the third test, which the Australians won by 82 runs to go 3-0 up in the five test series, and left the Adelaide Oval on crutches just five days before the next meeting on 26 December.
"It doesn't look great," said Cummins. "Don't know yet, but seeing someone on crutches doesn't really bode well for a test match a week away.
"(The) guy is pretty close to irreplaceable. The ability to make breakthroughs, but also control an innings, is really important, so he's going to be hard to replace.
"But we've got some guys who have already had a taste of international cricket around the traps, other guys have done really well in domestic cricket.
"It's been one of the benefits of the Sri Lankan tours, the West Indies where we take a couple of spinners. There's guys that can step in and you feel like it's not going to be too overwhelming."
Todd Murphy, Corey Rocchiccioli and Matthew Kuhnemann would be options to replace Lyon if the 38-year-old does not recover in time while Cummins is also likely to miss the Boxing Day test in Melbourne as he manages his own return from injury.
Steve Smith would be expected to return to the batting line-up after missing the Adelaide test due to vertigo and would take over from Cummins as captain again should the fast bowler decide not to risk his fitness ahead of the fifth test in Sydney.
A return for Smith could also lead to a shake-up of Australia's batting order after Usman Khawaja impressed having initially been left out of the side in Adelaide prior to Smith's late withdrawal.
Khawaja responded to his last-minute call-up by hitting 112 runs across Australia's two innings and that performance could increase the pressure on underperformers such as Josh Inglis and Cameron Green.
"We feel like we got enough batters there to choose from," Cummins said about his side's batting line-up.
"I think this game...we had a little opportunity to really bat them out of the game, and we didn't quite take it. But it was good enough."