Jos Verstappen has called on Red Bull to improve its car development after his son Max clinched his fourth consecutive Formula 1 drivers' championship in Las Vegas.

The elder Verstappen admitted he wasn't always confident Max's 2024 campaign would succeed, given the team's struggles with car performance and internal conflict.

"Max had a certain lead, of course, but it also depended on what they did with the development of the car," Jos told Viaplay. "My head was certainly not always positive about it anymore. But what Max ultimately showed, and the races he drove, is unprecedented. What he did in Brazil in particular got him over the line."

While Max Verstappen secured his title with a P5 finish in Las Vegas, Jos acknowledged that the Red Bull car is not currently the fastest on the grid.

"Red Bull doesn't have the fastest car at the moment, otherwise Max would be winning races," he explained. "The fact that he won the title in this car speaks for itself. Look at (Sergio) Perez's results. Something has to change for them to be competitive again."

Jos praised Max for his calm and focused approach throughout the season, attributing it partly to the tough lessons he taught his son during his early racing years.

"He was pretty relaxed about everything," Jos said. "And I think he is now reaping the benefits of being treated a bit harder by me. I think Max needed that learning experience.

"When you see how he is dealing with the pressure now, I can only be proud."

Despite his pride, Jos remains vocal about Red Bull's need to improve, particularly ahead of the critical 2025 season.

"The team knows what the problems are and what needs to change," he said. "Now they have to prove that they can cope with it.

"I want to see a fifth title next year," Jos added. "We started this season very well, but then we went backwards. Now it's up to the team to see how things go in 2025."

Jos has hinted this year at his openness to seeing Max explore other team options in the future, potentially with Mercedes in 2026. However, he emphasized Red Bull's responsibility to match Max's exceptional talent with a more competitive car.

"If Max has a somewhat good car, he is in contention," he said. "But it's up to the team to build a better car for next year, otherwise we're nowhere. It's certainly not Max's fault. Everyone knows that by now."

Reflecting on the Las Vegas GP, Jos said it was a challenging race to watch from home. "I didn't feel very well. I have a little flu, so I didn't want to be near Max," he explained. "I was nervous—I was already awake at 4am because I couldn't sleep anymore.

"In the end, it worked out. Not in the way Max would have liked, I think, but the most important thing is that it worked out."

Jos remains optimistic about the future but insists Red Bull must step up. "Max is the best in the world. This year's title shows once again how well Max is doing and how strong he is."