Nico Rosberg believes Ferrari is genuinely close to his Mercedes team after topping the times in second practice for the Austrian Grand Prix.
Sebastian Vettel put Ferrari on top of the times in FP2, outpacing Rosberg by 0.011 seconds while teammate Lewis Hamilton struggled and finished down in fifth.
Rosberg admitted Ferrari's pace was a worry.
"We are always worried about them as they are our closest rival, and here on this track it is a very short lap time so everyone is going to be naturally closer and they seem to be quick today," said Rosberg.
"They seem close. On this track everyone is a bit closer and they seem quick today."
Rosberg said that Mercedes still had time to be found, but conceded the team will need a flawless weekend in order to beat Ferrari.
"I always have a bit in my pocket on Friday," he said.
"On the long run they were even closer, but in general everyone is close here and we really need to do a perfect weekend."
Hamilton, meanwhile, admitted his day not been far from great.
"It has been okay. It's not been the best of days," he said.
"The car has been great, just the track there is not a lot of grip here."