Gradi accepts Miller has undoubted talent but he wants the player to produce the goods more regularly.
He said: "I still think Shaun can be our number one goalscorer but he has got to start doing well for me to pick him. He has played quite a number of games now and he needs to become more consistent.
"His all-round game has improved and hopefully now he can stay free from niggling injuries and start challenging for a place in the team.
"The other two deserve to be ahead of him at the moment because he has got to score goals on a regular basis."