Lewis Hamilton topped both sessions at Istanbul Park but will take a 10-place grid penalty after Mercedes opted to fit a new engine into the W12.
On whether Red Bull had expected the move this weekend, Horner said: "I think it was probably, from what we understand, a forced choice rather than a selected choice.
"We have seen they have had issues with some of their other teams as well. It doesn't affect us and what we are doing but it shows how tight and tough it is to get to the end of the season with three engines that neither of us have managed.
"Hopefully, we can do it on four."
What do you think?
I am sure they will get the balance right for tomorrow. Mercedes always in that boat, trying to get their set up right.
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