Daniel Ricciardo qualified his opening day of free practice at Paul Ricard as "productive", but fears Red Bull could be left chasing a very fast Mercedes squad in France.
Ricciardo and team mate Max Verstappen clocked in second and third in Friday's afternoon session, the Aussie finishing 0.704s adrift from Lewis Hamilton, the man at the top of the time sheet yesterday.
Ricciardo felt his day of running had gone pretty much according to plan, but a glance at Hamilton's pace instilled a sense of wariness and the belief that hard work remained ahead.
"I thought we were relatively fast, but then we saw the time of Lewis and the long runs were a bit more up and down," he said.
"We have a bit of work to do tonight but it wasn't a bad Friday actually. The time to Lewis in this session (FP2) now was a bit too big, but actually our day was pretty productive.
"Obviously Lewis was pretty quick, that’s a bit of a shame, he obviously did a good lap."
"Hopefully they used it (the new engine) today. If they’re going to go quicker, then it looks like everyone is chasing them this weekend.
"I guess for them it’s working. I don’t know where Valtteri (Bottas) was but obviously Lewis’ time was pretty fast."
Mercedes' drivers were indeed powered by the manufacturer's latest spec power unit, as the team confirmed after yesterday's second session.
Ricciardo is determined to focus on improving his own performance however, and sees a margin for progress, perhaps by tweaking the RB14's aero levels.
"I think we can keep improving. Today was a good day to get a lot of information. I think the downforce level is a question mark.
"Maybe we have a look and change that. I think it was a good Friday so hopefully it will be a better weekend.
"I think (we can learn) quite a bit. Across cars we changed a few things for this afternoon so I think we got a good bit of data to look at between myself and Max to try and figure out a direction.
"Downforce levels is a big one, so that’s probably one of the big things we will assess tonight to try and learn which way is better."
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