With the Asian Cup looming for Australia in January, Cahill is an odds-on prospect to captain his country in Qatar.
Moyes insisted he would not stand in Cahill's way should he choose to play for his country, saying: "If it comes in under the FIFA regulations we always abide by them.
"We admire Tim because we've all travelled out here from England and our players are all still in their beds with jetlag."
"For Tim to travel out here and play (for the Socceroos) and then return to play in the Premier League is an incredibly hard thing to do. It should never be underestimated how difficult that is."
On Cahill's dismissal against Germany, Moyes added: "When I saw the sending off I thought it was a terrible decision.
"Tim prepared all through the year. To get sent off for that could have ruled him out of the whole World Cup."