Cahill struck in their 2-0 win at Birmingham City.
Moyes admitted that goalscorer Cahill, who nodded in Leighton Baines' cross to seal the win, has still not fully recovered from his recent knee problem.
He said: "There was a doubt about Cahill. He is still not looking 100 per cent.
"He has not trained enough for me to think everything is absolutely right."