Houllier is attending the Soccerex this week.
"I look at Ronaldo at Real Madrid and I'm very surprised by the quality of his desire every year," Houllier told Reuters.
"He is scoring practically 50 goals a season over several seasons, not just one year. It is remarkable.
"You need talent, work and a great attitude - attitude makes the difference. Your attitude can compensate for a little less talent.
"If you don't have the desire to go with the talent, it makes it hard to succeed.
"It is about how you behave off the pitch and how you train on it. Once a player understands that maybe he doesn't have the same talent as his neighbour but that he can make up the difference, it helps."