The German, who was outpaced by teammate Kimi Raikkonen in both sessions, lost track time following a small problem on the left rear wheel in FP1 and ended up four tenths off the pace in FP2.

"I'm not happy," Vettel told reporters at Barcelona. "I'm struggling a bit to find the rhythm, I'm struggling a bit with the conditions, probably more myself than the car.

"I didn't get everything together, I wasn't too happy but I can feel the car is quick so that is good. I'm not worried, I'm just not happy with how the day went.

"I wasn't always feeling like I was captain onboard. Sometimes somebody else was steering my ship and I hope tomorrow, whoever that was, will disappear."

The championship leader said everyone was struggling with the tyres and backed up rivals' claims that the compound choices are too hard.

"Today was quite a shocker, if you look at the long runs," he said. I had a very short glimpse and everybody was struggling with the conditions. I was on the medium, it was quite slippery - very interesting.

"Other people suffered a lot with degradation on the soft. Generally, tyres feel a bit hard - I don't know why. I think it's the myth of Barcelona where maybe Pirelli is a bit afraid.

"By Sunday, things calm down and the track picks up and it should be OK."

Vettel said there is more to come later in the weekend and added he was pleased with the update package Ferrari had brought to Spain as the outfit looks to maintain the challenge to Mercedes.

"I don't know what Mercedes is up to," he said. "It looks like it will be between them and us. I think there was quite a lot left on the track, which I didn't get to and which I didn't find yet so I'll have to look tonight.

"I don't know who brought the most updates, I don't think it matters who brought the most, I think it matters who brought the best.

"I'm happy with what we brought, some of the stuff you can see, some of the stuff you will not see. There are no secrets but usual work."