Verstappen was handed a Red Bull race seat after the Russian Grand Prix, with Daniil Kvyat demoted to Toro Rosso after causing multiple collisions at the start of his home race. Verstappen duly won in Barcelona and has been a threat in a number of races, with his defensive driving coming under criticism at times from the Ferrari and Mercedes drivers.
However, Horner believes the negative comments are a result of Verstappen emerging as a new threat to those chasing wins and championships, but has been impressed by the way the teenager has ignored his critics.
"I don't really understand what they are moaning about," Horner said. "He is doing a great job and driving the wheels off the car and he is racing hard.
"When sometimes a new guy comes along and upsets the establishment a bit then they do get a bit of criticism. He is not rising to that. He is keeping his head down and enjoying his racing. Anything that de-stabilises an established pecking order is always not well received.
"I don't think he has done anything wrong. He has raced hard, he is exciting and giving it everything every time he is in the car, and he loves what he is doing. He is passionate about it."
Verstappen's approach won him two awards at the FIA Prize Giving this month, with the Red Bull driver winning Action of the Year for his move on Nico Rosberg in Brazil, and also Personality of the Year.