Jos Verstappen has been vocal over his concerns with Red Bull this seasonMax Verstappen has failed to win eight times this season, five more than last year
Speaking to Bild newspaper, he said: "Over 20 seconds is a huge disappointment but that's not surprising when you reverse engineer the car.
"The team has taken the wrong turn several times. Internally, they should hold up a mirror and not always sugarcoat everything.
Red Bull's lead over McLaren in the constructors championship has been cut down to just 30 points
"It's time—if it's not already too late—to question themselves. The good people are leaving the team. I'm very unhappy with what's happening because Max cannot be happy with a car like this.
"Now it is up to [Christian] Horner to get the team back on track. I'll be surprised if he does. A lot has to happen for that. The whole spirit has to change."