The Faenza-based squad slipped behind McLaren to seventh in the constructors' standings in last weekend's Spa race, the second in succession that both Sainz and teammate Daniil Kvyat have failed to score.

While Kvyat finished in 14th, Sainz was running seventh when his rear-right tyre delaminated in spectacular style along the Kemmel Straight at the start of the second lap.

While the Spaniard believes that he never had any real chance of scoring points, such was Toro Rosso's lack of pace, he says that the STR11 was struggling just as much in the corners as it was in a straight line.

"We have a limitation on the power unit side, but it's something we expected and something we were prepared for," said Sainz.

"We put an upgrade at Hockenheim to compensate for the power we're losing, but since Hungary we have not been performing as we should have.

"So there are some question marks in the team to see why we have been suffering so much these last couple of races. Hockenheim should have been such a good track for us but it was similar to here.

"We look at the data and we see we are not really performing in the corners where we used to perform, so there's an issue there somewhere that the team will investigate."

Tyre trouble

Elaborating further on Toro Rosso's cornering woes, Sainz added: "The main feeling is that the balance is there, but then we look at the corner speeds where we were strong a few races ago, Silverstone for example, and we are not fast any more in these kind of corners.

"It's not like Force India, or Renault, or Haas have suddenly brought a new package suddenly to beat us in corners suddenly.

"Also I would say we have massive tyre degradation nowadays. Before we were not so bad, but now we cannot control the temperature of the rear tyres in the race.

"There's the tyre question mark, why the temperatures go off the chart, and why we are not quick in high-speed corners also."

Additional reporting by Oleg Karpov