The 27-year-old was desperate to play for his country, and Everton's medical staff monitored his recovery both on Merseyside and in Australia ahead of the tournament.
The Australian international barely figured in the competition, being used primarily as a substitute, before heading back to Everton for further treatment.
Since then he had been out until Thursday's UEFA Cup tie with Larissa, won 3-1 by Everton with Cahill scoring the opening goal.
Now Moyes has vowed to keep a careful watch on the midfielder's recovery to make sure he does not have any further relapses.
Moyes said: "Against Larissa, he showed how important he is for us with his goal, and he gives us something different.
"Tim has been missing since the beginning of the season, and he fought to get himself fit to play for Australia in the Asian Cup in the summer.
"Maybe in hindsight that was too soon and it had an effect on his recovery."
He added: "That was probably the wrong decision and he should have had a bit longer to get himself ready for matches.
"But he played, and got injured in his first game back for us in a pre-season friendly against Werder Bremen.
"He was desperate to get back into action, and it is the same now. But we have to be careful with him.
"We continually hear these days how these metatarsal injuries keep coming and how easy it is to do more damage, so we will watch him and nurse him along.
"He is different to what we have. He can play virtually up front, but coming from deep it is hard for defenders to pick him up.
"He trained okay on Friday and he seems fine. He could be in contention if we think it is right."