The Moroccan striker has scored just once for the Eagles since making the switch from Arsenal in the summer and has now gone eight games without a goal.
Caretaker boss Millen believes the solution may be for Chamakh to try and conserve some energy and be more selfish in front of goal.
"When you look at his stats he works harder than anyone - probably too hard sometimes," Millen said in the Daily Star.
"Sometimes he does running for the team that he doesn't need to, so when he does actually get the ball he's tired. So I have been trying to say to him, 'Cut down the running and get in more dangerous areas'.
"I'm trying to get him to think about scoring goals more and be a bit more selfish."
Millen has been impressed by Chamakh's enthusiasm but recognises that it must have been difficult for him to adjust to playing for a club struggling near the bottom of the table.
He added: "I'm sure it has been a bit of a culture shock for him, coming here from Arsenal.
"He was out of favour at Arsenal at the end and he feels this has given him a new lease of life.
"When you think where he's come from, to a team that's struggling, you couldn't ask for any more."