The Chelsea-owned goalkeeper kept the Barcelona ace out six times last season, so he has no qualms about facing the No.10 in Brasilia on Saturday.
The goalkeeper faced the Barcelona attacker six times in the colours of Atletico Madrid last season and did not concede a single goal to the four-time Ballon d'Or winner.
As a result, facing Messi in the last eight of the World Cup holds no fear for Courtois.
"I know him well from Atletico's games against Barcelona, so it'll be nice to play against him for our countries," the 22-year-old told reporters in Salvador after helping his national team claim a dramatic 2-1 win over United States in the round of 16. "Hopefully we can win, but we'll see. The good thing is that I don't have to watch videos of him because I know him so well.
"But even if you watch videos of him, he's so unpredictable that it's impossible to study him to know what he's going to do. As soon as he finds a way to shoot, he will shoot, so the only thing you can do as a goalkeeper is concentrate at all times.
"You can't think of anything else for one second because at that moment he will score."
Courtois' remarkable powers of concentration were very much in evidence at Arena Fonte Nova. Unlike his American counterpart, Tim Howard, the Chelsea-owned shot-stopper had been given very little to do during 90 scoreless minutes in Salvador.
However, he proved his class in the closing stages of extra time after USA had brought the game back to 2-1, pulling off a fantastic close-range stop from Clint Dempsey that effectively earned his country a place in the quarterfinals.
"I think that maybe we started the second half of extra-time without enough pressure on the ball," Courtois mused. "We let them play too easily and they had the quality to score a goal. Then they kept coming at us but I think I made a good save from Dempsey at the end.
"Maybe after we made it 2-0 we thought that the final 15 minutes would be easy. But I knew it would not be like this. It's a World Cup; it's always hard. And once they made it 2-1, it was very difficult. But we stayed strong and managed to win."
Belgium are now just three wins away from World Cup glory but Courtois, unsurprisingly, is not looking beyond Saturday's date with Messi in Brasilia.
"Winning this tournament would be incredible but we have to go step by step - and the next step is Argentina," he pointed out. "So let's try to get by them first and then see what happens in the future. But it's going to be really hard to beat Argentina."