"(FIA race director) Charlie (Whiting) was keen to show him a replay of Spa," Horner told Sky Sports television at the Italian Grand Prix.
"It was a gentle warning to say 'that''ll be a black and white flag'...a bit of a warning."
A black and white flag can be waved, once only, at a driver during a race to warn him that he has been reported for unsporting behaviour.
If the driver does it again, a black flag will be shown which tells him he has been excluded and must return immediately to the pits.
Verstappen tangled with Ferrari drivers Kimi Raikkonen and Sebastian Vettel at the start in Spa and then aggressively defended against Raikkonen when the Finn tried to pass later in the race.
Raikkonen, the 2007 champion, accused the 18-year-old of forcing him to brake by changing position and expressed concern that he had acted in that way as payback for what had happened earlier.
The Formula One paddock has been divided by Verstappen's actions, which were not punished by race stewards at the time, with some feeling the Dutch youngster had done no wrong while others condemned him.
"In the middle of the straight you are allowed to do one move as long as the other car is not alongside you," commented McLaren's double world champion Fernando Alonso, who felt Verstappen had not broken that rule.
Whiting met the two Ferrari drivers on Thursday and will talk to all of them later on Friday in the regular pre-race briefing.
Horner said Verstappen, the youngest race winner in the sport's history and already attracting a considerable following as a rare talent and rising star, cared little about what the others thought.
"Like any 18-year-old, (the criticism) seems to be going in one ear and out the other," he said.
"He really doesn't care, he's focussed on his own job, he's not intimidated by the surroundings he's in and I think that's what marks him out as a real talent and star of the future."
(Editing by Ed Osmond)
