Houllier said: "Michael will come good, you can be sure of that. In fact, he will definitely score against Croatia and England will qualify.
"Perhaps he may have to develop his game because at the moment he is finding it very difficult against two banks of four defenders in each game. It's the same for all the big strikers like Thierry Henry, Raul, Christian Vieri. They are all struggling and have yet to score because everything is so tight in this tournament. If they are there on their own then they are constantly surrounded by defenders.
"Michael may find he has to come short for the ball or spin out wide to lose his man and then be able to work on an understanding with Rooney.
"I'm not worried that he hasn't scored yet because with Michael you always know the goals will come. I've spoken to him and his confidence is still high. He doesn't appear worried himself."