Max Verstappen's father and co-manager has spoken out to question the legality of championship rival Lewis Hamilton's Mercedes car.
Referring to last weekend's grand prix in Brazil, Jos Verstappen told De Telegraaf newspaper: "I have never experience such a speed difference from one race to the next in my whole life."
Indeed, a fresh engine was installed in championship chaser Hamilton's car at Interlagos, resulting in a straightline speed advantage approaching a reported 30kph.
"Obviously you can fine-tune a new power unit like that a little, but does a new Mercedes really degrade after two or three races like they say?" Verstappen added.
"I can't imagine that."
Red Bull, who are hinting at a protest, also suspect the rear wing of Hamilton's car is flexing at high speed, leaving telltale "score marks".
And video footage from Interlagos has emerged depicting Hamilton's steering wheel moving slightly backwards and forwards, raising questions about a secret adjustable ride-height system.
"A steering wheel is there to turn left or turn right, so why would it move from front to back?" Verstappen snr, 49, told the Dutch newspaper.
"You can see that something is going on. After the race in Brazil we also saw Hamilton get handed something from his trainer and then going back to the cockpit.
"I'm very curious why that is," said the former Formula 1 driver.
"If you add everything together, it's just weird that they're suddenly making such a difference at this stage of the season.
"It seems to me very strongly that they are doing something that is not allowed. I don't want to lose, but it has to be fair," Verstappen said.
Jos also confirmed earlier reports that his former relationship with Mercedes team boss Toto Wolff broke down completely after Max's controversial crash with Hamilton at Silverstone.
"We haven't spoken since then," he said, having been upset at Mercedes' wild celebrations while Max was in hospital. "His true nature has come out this year.
"We no longer have any contact with each other," added Jos.
