With Lionel Messi having put the ball through his legs on two occasions, Courtois faced plenty of uncomfortable questions afterwards.
Former Barca and Manchester United boss Van Gaal was among those to speak out, telling Ziggo Sports: “The game was turned upside down due to the blunder of Courtois [for Messi’s first goal] which I think is a big blunder.
“If he’d have had [Dutch former Manchester United goalkeeping coach] Frans Hoek as goalkeeper coach, he would have closed his legs.
“That just should not be allowed to happen.”
Van Gaal was not the only one to make such comments, but Courtois has taken issue with seeing his attributes questioned by a man with no goalkeeping experience.
He told Sporza while away on international duty: “When I hear so-called experts talking, I think they know nothing about goalkeeping — for example, Van Gaal should not talk about goalkeepers.”
While frustrated to see his failing thrust under the microscope, Courtois concedes that he is not without fault and that Messi has made a habit of showing him up down the years.
He added: “I have often played against Messi and it was not the first time he scored with a shot between my legs.
“For a goalkeeper of my height it is probably my weakest point. That is very annoying, but I have to face it. I have to acknowledge my mistake as a man.”
Belgium are back in action on Tuesday against Saudi Arabia while Chelsea’s first game after the international break will see them welcome London rivals Tottenham to Stamford Bridge, but Courtois is doubtful for both of those contests after picking up a hamstring injury.