Hamilton and Verstappen came together on lap 26 at Monza, as the two were battling for position heading into the chicane at Turn 1.
Verstappen bumped along the kerbs, with the Red Bull propelled into the air, landing awkwardly on Hamilton’s Mercedes with both cars beached in the gravel.
Verstappen subsequently was handed a three-place grid drop for the Russian Grand Prix, something Horner didn’t agree with.
“My opinion of that incident is unchanged to when I saw it. For me, it was a racing incident that Max saw a gap,” Horner told RacingNews365.com. “It was an aggressive move, but we’ve seen moves happen there throughout the weekend.
“And, of course, Lewis didn’t want to concede track position, they both knew what that meant. “So you had two drivers desperately wanting to defend and one to attack and the outcome was, unfortunately, what we saw there. “It was just unfortunate the way the car rolled up and making it more dramatic, obviously, at a low-speed corner than you could have imagined.”
Verstappen’s Red Bull was left wedged on top of the Mercedes, as Hamilton desperately tried to reverse the car to rejoin the race.
Verstappen meanwhile climbed out of his car and made his way straight back to the garage with his helmet on.
Hamilton reported he had a “huge headache” after the incident, which saw Verstappen’s right rear tyre graze Hamilton’s head, but both cars looked relatively unscathed.
“There was some floor damage, some front wing damage but, other than that, it was minimal,” added Horner.
The incident marked the second time this season the pair had banged wheels, with Hamilton handed a ten-second time penalty for the 51G impact Verstappen suffered in Silverstone.
The Dutchman was sent to hospital after the crash, in the race won by Hamilton as the two teams locked horns over the incident.
Hamilton branded Verstappen’s driving style as “aggressive,” however Horner said his driver knows that they are playing the long game as Red Bull try to pick up their first driver title since 2013.
“I think he gets that. Absolutely,” said Horner. “But I think he’s also a racecar driver. If he sees a gap, he is going to go for it. And I think you could argue it the other way around [with Hamilton] as well.
“You [have] got to grab every opportunity you have. “I think that Max has driven incredibly well this year. He’s had bad luck.
“In Baku, obviously in Hungary, I think at Silverstone he was very unlucky. But that balances itself out over the course of a year on average.”
Verstappen leads the way by five points heading into the Russian Grand Prix on Sunday after picking up two extra points during the Italian Grand Prix sprint qualifying weekend.
Mercedes meanwhile lead the way by 18 points in the constructors as they look to secure an eighth back-to-back world title.