Toro Rosso Team Principal Franz Tost admits he expects the junior Red Bull outfit to struggle over the next two Grand Prix weekends, starting with Sunday's race at Spa-Francorchamps in Belgium.

The Italian team has had a quiet season, with a strong showing in Monaco the only significant highlight, yet the consistency of highly-rated Spaniard Carlos Sainz has still shone through with points finishes at every race in which he has finished so far in 2017.   

But in that fact also comes the weakness of Toro Rosso with the Renault power unit proving both unreliable and underpowered compared to most of their midfield rivals. The lack of performance is what Tost points to as the main reason for his pessimism over their chances at Spa and the following race in Italy just seven days later.

"Mid-fast and mid-slow corners are where our car is working quite well, where the engine is not the priority as it is in Canada, Austria, Baku or Silverstone," Tost said.

"I expect once we are in Singapore, America, hopefully also Japan we will be will be quite competitive. I expect problems in Spa and Monza because they have such long straights where you simply need the engine power and we all know that we are down there a little."

For their part, Renault, who have previously stated their focus will be on small updates rather than larger changes much to the frustration of their Red Bull customers, revealed such updates would be coming for two of the most power-sensitive circuits on the calendar.

"Spa and Monza will see new software and hardware updates," said the boss of Renault's engine operation Remi Taffin. "We are looking at Monza as a benchmark as it could provide a clear picture of the ranking of the engines.

"After Monza, we have more races and more things in the pipeline, the next two months will be important for the 2017 season outcome," he added.

As for Toro Rosso, they currently sit sixth in the Constructors' Championship but face a significant battle with Williams, Haas, Renault and maybe a resurgent McLaren over the final nine races. A key element in that fight will be car development as some stop to focus on 2018 and others, like the Faenza team, simply have to manage their finances.

"We've upgraded the car, we made some progress, but we are also from this end budget limited," Tost revealed. "We cannot come up, like the top teams, every race with a lot of upgrades because they have three or four times the money of us.

"We really have to calculate always what we do, how we do it, and so far, I must say we have done a reasonably good job."