"To be honest, we didn't anticipate quite such difficulty. It was worse than we expected," he told AutoSport.
"We knew before we went there that if we could get on top of things there, it would be a pretty encouraging sign.
"But I think we're not far off because in the second half of the race when it cooled down a little bit, Lewis was able to pick the ball up and run with it again. He had certainly struggled in the first half of the race."
Sebastian Vettel triumphed last weekend.