Following Ferrari’s failure to win the world championship this year, Binotto offered his resignation after feeling he did not have the full support of the Italian manufacturer’s senior management team.
Ferrari accepted his decision to quit and is currently finalising a replacement, with Alfa Romeo team boss Frederic Vasseur favourite to take the job.
Binotto’s departure could disrupt the form of one of Red Bull’s chief rivals, with Horner conceding the good job the Swiss-born Italian had done at Maranello.
Asked by Motorsport.com at the FIA Gala Awards in Italy if he was surprised by the events at Ferrari, Horner said: “I think, in all fairness to Mattia, he did a very good job in producing a very competitive car and engine for Ferrari, certainly this year. Obviously, they had their moments operationally.
“He committed a long period of his career and life to Ferrari, and I'm sure it must be very difficult for him to leave that team after all of that time.
“So, of course, a huge pressure in that team, because it's a national team effectively, as well as an OEM team. And I think that it will now be the sixth team principal that I will sit across the table from, since I've been at Red Bull and, obviously, you know, a lot of pressure on that job.”
Horner attended Friday night’s FIA gala to collect Red Bull’s first constructors’ championship trophy since 2013.
Reflecting on the battle with Ferrari this year, he singled out Max Verstappen’s victory at the Emilia Romagna Grand Prix as a key moment in getting Red Bull’s championship ambitions back on track after a difficult start to the year.
“I think they [Ferrari] had a faster car than us in the early part of the season,” he said.
“But we were able to stay in touch and that was very, very important.
“Our championship was 21 races, because we missed the first one by having a double DNF. But we had to stick with them.
“And, for me, one of the crucial weekends was Imola with the sprint race, and then the victory. To win both those races to achieve the 1-2 finish and to beat Ferrari on their home ground was, I think, psychologically a big thing for us as a team, potentially for them as well.
“I think then, as we developed the car, and we improved the car, and we lost a little bit of weight, then the speed came.”
