Although Williams did not come to the fore in Friday's practices in Hungary, Sebastian Vettel has warned against writing them off.
On a day when lap times can count for very little, Vettel was the closest challenger to the Mercedes drivers.
The Red Bull racer brought his RB10 home in third place, 0.629s off the pace.
The German, though, is wary of predicting that Red Bull are leading the battle to be the best of the rest, saying others teams especially Williams could still make inroads.
"I think we could be a little bit closer this weekend here, but we have seen a lot of people make big steps from Friday to Saturday - in particular Williams - so we have to be careful," he told ESPN.
"I think people gain more from Friday to Saturday than we do. We hope we have a big enough step to keep the pace of today."
The four-time World Champion weighed in on improvements from Renault, stating that while they had little impact last weekend in Germany, he is hoping for better from the engine supplier this weekend.
"In general Renault and Total are pushing really, really hard. Last weekend we were expecting an upgrade which just didn't bring the advantage we were looking for.
"Tomorrow we should have a bit of a step up between Friday and Saturday, which is normal all the way down the pit lane, with people running fresher engines and able to use a little bit more power.
"We will have to wait and see where we are tomorrow."
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