Carlos Sainz says the whole Toro Rosso team is frustrated by its recent drop in pace and performance which he feels it needs to identify and solve immediately for a competitive end to the year.

The Spanish driver was given little opportunity to demonstrate the Toro Rosso's full potential at Spa after a rear tyre blowout on lap two forced him out of the race.

Looking at Daniil Kvyat's performance in the sister car, who finished 14th behind both Haas drivers and the sole remaining McLaren, Sainz conceded points were unlikely in Belgian because of the recent performance dip which has confused the Toro Rosso squad.

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After introducing an aerodynamic upgrade just before the summer break in the bid to resist losing speed due to its year-old Ferrari power units, Sainz says the SRT11's relative pace has dropped significantly and is concerned the cause may be coming from a range of issues involving tyres and aero.

"We brought an update to Hockenheim to compensate for the power loss we are losing," Sainz explained. "But since Hungary we were not performing as we should. There is some question marks in the air in the team to see why we are not taking the step with the performance upgrade and why we are suffering so much.

"We look at the data and we see we are not performing in the corners that we use to perform in. There is an issue there somewhere, which the team will look at and will investigate and hopefully we come up with a solution.

"The main feeling at the moment is that the balance is there but then we look at the data and we look at the corner speeds and where we were very strong four races ago, at Silverstone for example, and we are not strong any more in these kinds of corners.

"Also the degradation we now have massive degradation now, whereas before we were not too bad on tyres. We cannot control the temperatures of the rear tyres in the race."

Toro Rosso's aspirations of holding sixth in the F1 World constructors' championship took a hit after Fernando Alonso's seventh place in Spa saw McLaren move ahead of Toro Rosso in the standings.

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"Now we have to play catch-up," he said. "It is not good and I am sure they will not be happy at Toro Rosso. I am not happy. James [Key] will not be happy. Franz [Tost] will not be happy. We need to analyse and at least if McLaren do beat us, they have to beat us performing at the level we should be expected at, not performing like we have in the last couple of races."