The 24-year-old is still looking for his first goal for Liverpool since his summer move from Southampton, but Benitez insists the goals will come.
"He's a nice boy and sometimes he's too nice. As a centre-forward in England you must not be nice," said the Liverpool boss.
"You must be aggressive against defenders because they will be aggressive to you.
"He is a player with ability and players with ability sometimes find it hard to be aggressive. It is a problem, but a nice problem to have," added Benitez.
"It is a mental thing. It is difficult to change these things, but he is clever and knows how to do it.
"I am not worried when he will score, though. I am more worried about when the team will score."