Sydney, Jan 2 (AFP) Defending Asian Cup champions Australia were dealt a blow Wednesday with Hibernian striker Martin Boyle ruled of action for "an indefinite period" with a knee injury.

The Scottish-born attacker was shaping as a key member of the team after scoring two goals in three appearances since switching allegiances to Australia in November.

But he picked up a knock in their 5-0 rout of Oman in a warm-up game on Sunday and will miss the tournament.

"We sent Martin for a scan yesterday and the outcome of that assessment is that he will be out of action for an indefinite period," said Australia coach Graham Arnold.

"Martin was desperate to stay with us but we've decided that the best thing for his long-term career for both his club and country is for him to return to Scotland where he can receive great care at Hibernian FC."

Boyle, who qualifies to represent the Socceroos as his father was born in Sydney, said he devastated.

"The Socceroos have become a big part of my life in a short period of time and I'm gutted that I won't be able to be with the boys in the UAE at the tournament," he said.

"My focus now will be on my recovery and returning to the pitch as soon as possible with Hibs."

Australia, who are already without midfielders Daniel Arzani and Aaron Mooy due to knee injuries, will name a replacement in the coming days.

The Asian Cup kicks off in the United Arab Emirates on January 6 with Australia in Group B alongside Jordan, Syria and Palestine. AFP

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