Speculation is increasing that a technical controversy is behind Ferrari's sudden dip in form.

The Italian team were riding a wave of form this year until the last two races in Canada and Baku.

One suggestion is that an FIA clampdown about the adding of oil to fuel was specifically targeted against Ferrari.

"There is someone who is now with the silver team that came from the red team and knew what to look for," Red Bull team boss is quoted as saying by Osterreich newspaper.

The implication is that Mercedes raised the alarm about the 'trick' Ferrari system.

However, Dr Helmut Marko thinks that Sebastian Vettel is still the 2017 title favourite.

"Even though Ferrari apparently lost some engine power due to the oil in the fuel story, Sebastian is the strongest in the races," the Red Bull official told Kronen Zeitung.

Ferrari are 24 points adrift of leaders Mercedes ahead of this weekend's Austrian Grand Prix.