Lewis Hamilton has already used his three permitted power units for the 2021 season but could opt to take a punishment in order to replace the engine for a fourth time.
And with seven Grands Prix remaining and Hamilton just two points ahead of Max Verstappen in the title race, Horner believes Mercedes are waiting to pull the trigger on their decision.
Speaking after Hamilton won the Russian Grand Prix, Horner said: “We’re not privy to that kind of information.
“But you’d assume that [with] the amount of Mercedes engines that are being changed in their sister cars and customer teams, you’d expect potentially for there to be a penalty, but obviously we can’t rely on it.”
Red Bull adviser Helmut Marko then told Sky: “I hope that our information is correct. According to that, Lewis will have to change again. Going from last place on the grid to the podium doesn’t happen that quickly.
“The upcoming tracks are to our advantage, especially because of the altitude in Brazil or Mexico. We need to win again now, but feel strong enough and attack again.”
Verstappen came from the back of the grid to finish second at the Russian GP, losing just seven points to Hamilton in their battle for the championship.
The 23-year-old Dutchman is now two points behind Hamilton in the drivers’ standings but remains the title favourite with seven races remaining.
Next up on the Formula 1 calendar is a trip to Istanbul for the Turkish Grand Prix on 10 October.
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