Mercedes upgrade a 'worrying' step forward - Christian Horner

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Red Bull boss Christian Horner says Mercedes' latest engine upgrade is "quite worrying" after Lewis Hamilton won the Italian Grand Prix by 25 seconds from his nearest rival.

Mercedes spent seven engine development tokens ahead of the Italian Grand Prix, but insists the update was aimed at preparing the power unit for improvements in 2016 and running new fuel and oil rather than providing an instant boost in performance. Nevertheless, Horner, whose team is currently struggling with Renault engines that have not had tokens spent on them since the beginning of the season, believes his rivals have made a big step forward.

"It looked quite frightening on Friday and then obviously they must have had some kind of issue with Rosberg, because it looked like they wound the engines back a little bit," he said. "But certainly the step they made on Friday look significant, quite worrying. I mean, they're in a league of their own at the moment."

Red Bull was linked to a switch to Mercedes power units next year, but it now looks more likely that it will cut a deal with Ferrari. Maranello spent three tokens on its engine at Monza, but Horner suspects the Mercedes power unit is still significantly ahead.

"Ferrari, certainly in qualifying were closer than Friday suggested. Then in the race we saw the kind of pace that Lewis [Hamilton] had on a scrub prime tyre at the end there and it was pretty awesome. So I guess he was just managing the gap throughout the grand prix, so I think they're clearly someway up the rope."