Lemmens insists without Courtois, Real Madrid would be in serious trouble this season.
He told Sporza: "He is the best in the world, he is currently surpassing all his competitors.
"I watch almost all his games and he has been playing at a very high level for weeks.
"If he hadn't been there, Real Madrid wouldn't be where they are now. He's keeping them high on the table on his own, but winning the title as a goalkeeper on his own would be completely incredible.
"It's not easy to always keep an unbeaten goal.
"In Spain now they also write that he is 'the star' of the Primera Division. That means that he has surpassed (Leo) Messi. That is incredible."