"Everyone on our team realises it's possible. I think we have a strong squad with qualities that Spain will have to take into account,” he told reporters ahead of training on Wednesday.
“There are surprises in every tournament … the Champions League, the Europa League, the World Cup.
“There are always surprises, and I think we can be one of them. Eliminating the European champions would obviously be a huge upset. The confidence is there,” he said after a 4-1 victory over co-hosts the United States in Seattle on Monday.
Belgium bumbled through the group phase, eventually topping the standings after beating New Zealand 5-1 in their last fixture after being held by Egypt and Iran.
They then scraped by Senegal, coming back from two goals down with five minutes left to take the game to extra time and then win 3-2 with a last-gasp penalty.
"People were a bit disappointed in us, but we’ve set that right. We’re getting better and better,” Courtois insisted.
“Spain is the favourite, of course. They are excellent in possession, and when they lose the ball, they press quickly. That’s where the key lies: knowing how to quickly exploit the space behind their defence."
Spain substitute Mikel Merino earned them a 1-0 last-16 win when he scored against Portugal in the 91st minute on Monday.
“I think the goal against Portugal highlights their strengths," added Courtois. "We know Lamine Yamal is incredibly talented in one-on-one situations; he’s fast, agile, and can beat two players if necessary."
Courtois, rated among the best keepers in world football, knows all about the Spanish threat, having played at Atletico Madrid and Real Madrid.
"I've lived in Spain for 11 years; that’s a long time, of course. Life runs on a slightly later schedule there, and the weather is better. But ultimately, I remain Belgian.
“Spain is my second home, though, and I’ll probably keep living there after my career ends.
“I also have two children who are naturally more Spanish than Belgian, but at the end of the day, tomorrow's match is all about Belgium,” he added.
FIFA World Cup 2026
The 2026 World Cup is taking place from June 11th to July 19th in the United States, Canada and Mexico. The tournament features 48 national teams and is played at 16 modern stadiums.
Match schedule and times | Group standings and knockout bracket | How to watch the World Cup | World Cup Format | Past winners of the tournament
