Verstappen had just stopped for slicks on lap 22 when he emerged in third place on the still wet track, pushing hard to stay ahead of Ferrari’s title rival Charles Leclerc.
But as he accelerated up the climb, his Red Bull skidded and, correcting, he ran towards the yellow line which drivers must not cross.
Footage of Verstappen’s dashcam incident was shown during the Monaco GP and appeared to show him racing over it, but the view obscured how close his wheels were coming.
The matter does not appear to have been investigated by the FIA.
Perez had also stopped on lap 22 and, coming out of the pits, he also had a slide that sent him towards the line.
Perez’s incident was noted by FIA stewards at the time, but no further announcements were made about it during the race.
The FIA later announced that the two Red Bull drivers had been summoned by the stewards following the incident.
Shortly after the race, the Red Bull team principal was attending a press conference when he received a phone call from sporting director Jonathan Wheatley revealing that Ferrari had protested.
It came after Ferrari team principal Mattia Binotto said he believed Verstappen’s actions were against the rules.
“As Ferrari we are disappointed as we believe there has been a flagrant breach of regulations on the two Red Bulls for taking the yellow line when exiting the pits,” he told Sky.
“I think it wasn’t close. He was on the line and if you look at the sporting code, the wording says crossover.
“Then we had a clarification in Turkey in 2020 to avoid any discussion and if you look at the race driver’s notes it says keep to the right: so staying on the line violates the race director’s notes.
“I think each team has the task of following the notes of the race directors. It is clear and we are still seeking clarification with the FIA.”
Horner said Red Bull were confident Verstappen had stayed in the line, as regulations require.
“We stuck with all the footage we saw,” he said.
When asked if there were any discussions with the FIA about this during the race, Horner replied: “Nothing at all.”
Verstappen said the wild moment of the pit exit was a result of his super aggressiveness with his acceleration, which he said was crucial to staying ahead of Leclerc who was right behind him.
“I needed it,” he said of the push so strong immediately out of the pits.
“Otherwise he would have passed me, because I wouldn’t have the traction. Coming out of the pits, that was probably the most fun moment I had in the race trying to stay ahead.”