Max Verstappen was "grumpy" throughout the US GP weekend, Red Bull's team consultant Dr Helmut Marko has admitted.

With the drivers' and constructors' titles all wrapped up with several races to run, Dutchman Verstappen lost pole position on Friday with a track limits violation.

He then spun in the 'sprint shootout' before cruising to an easy sprint win, but on Sunday struggled throughout the US GP in Austin with brake problems - even though he made his way from P6 on the grid to the top step of the podium.

He was then booed by the American fans.

"In the end, I'm the one who takes the silverware home, so all fine by me," Verstappen insisted.

But as he struggled with the car's handling earlier on Sunday, cracks in the relationship with his engineer Gianpiero Lambiase emerged again.

Lambiase, having been chided by Max throughout the race, then told Verstappen on the radio "I'll see you on Friday" - as he skipped the podium proceedings and post-race debrief.

Asked to explain one angry outburst to Lambiase about not talking to him in braking zones, Verstappen hit back: "I said it nicely. At least I said please."

Dutch GP boss Jan Lammers thinks Max was right to chastise his engineer.

"When you're downshifting, it's important that you hear the revs properly, especially if you're having problems," he told NOS.

Team boss Christian Horner, meanwhile, denied that Lambiase actually boycotted the podium and post-race debrief.

"He just had to get back to England - he was rushing to catch his flight," he insisted. "Normally it's Helmut, but now it's the engineer."

Verstappen's father Jos also played down the obvious irritation of his son.

"The feeling wasn't there, so then you get things like this," he told Viaplay.

Marko also defended Red Bull's triple world champion.

"Max was a bit grumpy all weekend," the 80-year-old Austrian smiled. "I think he had to do too many PR activities, and that is never his favourite thing to do.

"He also couldn't drive consistently, because when he braked he had to wait and see what was going to happen," Marko told De Telegraaf newspaper.

"That made it very difficult for Max, but he still managed not to make a single mistake. It is unbelievable that he kept such a strong-driving (Lewis) Hamilton behind in those circumstances."
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