Sauber boss Monisha Kaltenborn confirmed at Suzuka that the Swiss squad will opt for the latest spec of the 2016 Ferrari power unit in 2017, explaining that the team had decided to "focus on chassis development and performance development" instead of adapting to any potential off-season changes to the engine.

Sainz's current team Toro Rosso has wound up using year-old Ferrari units this year and has, as a result, dropped down the competitive order as the season went on and upgrades for current-spec engines were introduced.

Asked about Sauber's engine decision for 2017, Sainz said: "Well, I wish them good luck.

"Normally they're one step behind, and if they have a fixed engine for the rest of the year, they will end up being two steps behind.

"Not an easy one for sure, but we want them behind so it's better for us."

Speed deficit "very frustrating"

Toro Rosso, which scored just two points in the last six races, could not seriously challenge for the top 10 in the most recent grand prix at Suzuka.

And, after he finished only 17th, Sainz lamented the straightline speed deficit caused by the year-old engine, saying it restricted the team's strategy options by making it "impossible" to overtake and very difficult to defend position.

"It's very frustrating, I must say," Sainz conceded after the Japanese GP. "I tried everything I could, everything - you cannot imagine. With the DRS, with the lines - I even passed [Esteban] Gutierrez one time round the outside of Turn 6, because it was the only place I could pass today.

"It's very frustrating, because you know when you go into a race also, your strategy is fixed, because you cannot overtake. It's a shame.

"It's frustrating, but it's what we have at the moment. We need to adapt, we need to correct it.

"[At Suzuka] we chose to run our standard downforce, without any compromise for our top speed - and it shows that our qualy performance improved compared to Malaysia, but our race was probably worse, so we'll need to analyse."

Additional reporting by Jonathan Noble