Toro Rosso can't be sure F1 tyre dramas fixed - Carlos Sainz

Sainz's team-mate Daniil Kvyat's participation in Friday's first practice session was cut short when he picked up a left-rear puncture and parked up on track after just four laps, and he suffered a second deflation in FP2 that caused him to spin at high speed.

Toro Rosso came to a decision with the FIA to stop running in second practice on safety grounds as a result of those punctures, and then worked to negate the chance of further problems - with the FIA clearing the cars to run on Saturday.

But Sainz, who suffered two punctures of his own at Austin, said while the team had done all it could to modify its cars suitably, including physically trimming back some of the bodywork, he couldn't be completely sure that a similar failure would not happen again.

"The team has put all of its available resources on fixes to the car to make sure we don't have any contact with the tyre and the rim," said Sainz.

"We've done everything we can, but the problem still is that we don't know the cause of the punctures.

"You're always going to try to tune the whole car up to make sure it doesn't happen, but without knowing the cause you're not going to be 100% sure it won't happen again.

"[The FIA] is happy because it sees the tyres are not exploding and also we can see less indications of problems in the tyres, [no sign] of contacts, so we are happy and confident - but we are not yet 100% able to say nothing's going to happen tomorrow."

Sainz qualified 21st, four places behind Kvyat, but he said that his concerns about the tyres had not crossed his mind while driving the car.

"When you jump in the car and you start a flying lap, you don't think the tyre is going to blow up," he said.

"It's lost in the back of your mind and you don't even consider it.

"What does happen is obviously your preparation for the weekend [is disrupted].

"You don't have time to think about the last detail that gives you the last two tenths."