Red Bull advisor Helmut Marko has revealed that Max Verstappen was "unwell" during the United States Grand Prix at the weekend.
Sergio Perez was visibly struggling post-race and Marko has confirmed Verstappen was not feeling 100 percent despite converting pole position to victory to extend his lead in the Drivers' Championship to 12 points over Lewis Hamilton.
"During the race it turned black in front of his eyes," Marko told Auto Motor und Sport.
"It's incredible how much mental capacity Max still has. He drives a car at the limit despite feeling unwell, but also still thinks about the strategy.
"Max brought himself back into shape with breathing exercises and drinking."
RacingNews365.com has learned from sources that Verstappen's complaints during the weekend were minimal.
Perez's illness affected him more and he was hindered further because he completed the 56-lap Grand Prix without a working drinks system. The Mexican described the experience as his "toughest race ever".
Marko believes Perez's and Verstappen's performances should be rated more highly due to both drivers not being at full fitness.
"For Perez, too much water flowed in the warm-up lap [in his car]," said Marko. "The stuff splashed around like the devil.
"Then he had to change the balaclava. He had no water in the race. When changing the car, to have less water, something went wrong. So that was a good performance.
"The performance of both [drivers] is to be valued even higher."
F1 Podcast: Were Mercedes caught out by Red Bull's aggressive strategy call in Austin?
It's time for the latest episode of the RacingNews365 podcast, with F1 journalists Dieter Rencken, Thomas Maher and Mike Seymour discussing the tense strategy battle between Mercedes and Red Bull and much, much more from the United States Grand Prix.