Manager David Moyes is concerned over a knee injury that could sideline Cahill at Birmingham today and affect his trip to play for Australia at home to Paraguay next Saturday.
But it is a recent change to the Socceroos' calendar that is causing Moyes most anxiety, as they will now play the Asia Cup in the new year.
Australia's switch from Oceania to Asia may offer them an easier qualifying route to the World Cup but has done Everton no favours, as their free - scoring midfielder is now likely be absent over Christmas and throughout January.
"Tim has trained, but I'm worried about his knee," said Moyes. "We'll see if he plays against Birmingham first, but we probably need to have a bit of a chat about the Paraguay game.
"The bigger issue is the Asia Cup, because we stand to lose him in the same way we lost Joseph Yobo to the African Nations.
"We've got to respect football in every part of the world, not just in our continent. But I think, in the same breath, there has to be some consideration for the clubs who are paying these players an awful lot of money.
"We could lose a player who's just been given a four-year contract and suffer financially and in terms of league position while he's away. The time may be approaching where this is all brought into line, or clubs are going to start asking to be reimbursed.
"I don't think a manager will be able to prevent a player going, but you wonder whether future contracts may stipulate that anyone from Africa, or maybe now Australia, won't get paid by their clubs for these extended periods on international duty."