Led by three-time world champion Max Verstappen, the Milton Keynes-based outfit have opened up a 56-point gap over Ferrari at the top of the leaderboard, but the dominant Dutchman has shown some glimpses of vulnerability in recent weeks.
Lando Norris pulled off one of the biggest shocks in recent memory at the Miami GP, as he raced away from the championship leader to clinch his maiden win in F1.
The McLaren driver then followed up that triumph with a fine performance in Imola last weekend, pushing Verstappen all the way as he came home in second.
With back-up driver Sergio Perez continuing to deliver inconsistent results, there is fresh hope that Red Bull will finally have to face a substantial challenge to their throne after enjoying almost three years of success.
Speaking ahead of the race in the principality, Horner has admitted that he's been impressed by the progress being made at McLaren, but also refused to rule out the possibility of Ferrari building on their recent improvements this weekend.
"I think you have got to say McLaren [will be the main threat] - they have a very fast car at the moment," Horner told media in a press conference.
"[Oscar] Piastri looked quick at certain moments, Lando was very quick at the end of the race there.
"The philosophy is very similar to that of our own. We expect them to be competitive at all circuits.
"But Ferrari are in the noise with them as well so that is another four cars we are up against, which is great for you guys!"