McLaren, Ferrari and Mercedes have formed a secret pact to try and catch pace-setters red Bull, according to reports in Germany's Bild-Zeitung newspaper.
The unconfirmed reports suggest the trio have agreed to exchange data on Red Bull, in a bid to overhaul its superiority.
Ross Brawn told Bild: "In some areas Red Bull have gone in different directions. Our people are looking at it closely."
Ferrari's Stefano Domenicali added: "This is a reference for us. We are not overstating it but we have to look more carefully at it and understand."
However, there looks to be little prospect of a respite for Red Bull's rivals; reports suggest the team is developing its own F-duct system to improve its cars' straightline speed in time for the Turkish Grand Prix later this month.