Carlos Sainz has claimed Red Bull has managed to develop the RB18 more than Ferrari expected would be plausible within F1's budget cap.
Red Bull is awaiting the findings of the cap's policing process to find out whether there has been a material breach of the financial regulations.
The certificates of compliance were scheduled to be released on Wednesday ahead of the Japanese Grand Prix weekend, only for the FIA to push the date back until the Monday after the race.
Red Bull has stolen a march on the Scuderia since the summer break, with Max Verstappen and Sergio Perez winning all four of the grands prix between them.
On the reasons for Ferrari's slump, Sainz said: “We are still working on it.
"We know that Red Bull is particularly strong in the race and we want to keep exploring that and keep improving our pace in those circumstances because it is where the points are made.
“We know we have a very strong car in quali but in the race is where we are focused on and this weekend we hope we can do another step like we did in Monza and Singapore and put ourselves in the fight for a win.”
Sainz - "Difficult" for Ferrari to keep up
The main concern over Red Bull's potential breach of the budget cap comes with the scope an overspend would assist the development of its car.
On whether the pace advantage seen recently was down to Red Bull improving or Ferrari falling back, Sainz replied: “If I knew, I would already have the solution.
"During a Formula 1 year, it is normally a combination of both, but normally Red Bull moving ahead and us, obviously, trying to keep up on development.
“But they have developed the car a lot, more than we expected that you could do in a budget cap situation and they have been developing just incredibly fast and fast moving.
“We try to keep up but sometimes it is difficult.”