Red Bull have hit back at any suggestion that their 2016 car may be illegal.
The team have sped past Ferrari in recent times, with Max Verstappen qualifying on the front row at Spa before teammate Daniel Ricciardo went on to split the Mercedes on the podium.
Asked if Mercedes are now in Red Bull's sights, even on circuits with long straights like Spa and Monza, Australian Ricciardo said: "Hopefully.
"It's been three podiums in a row so we're definitely making inroads."
However, Auto Bild reports that some of Red Bull's closest rivals are pointing fingers at the Renault-powered team's diffuser design.
TV replays from Friday practice at Spa reportedly depicted the diffuser flexing both vertically and horizontally.
The German report claims that Ferrari asked one photographer at Spa to "look closely" at the Red Bull design.
However, Red Bull's Dr Helmut Marko insisted: "Our car is completely legal and anything otherwise is just slander."
The season continues on Sunday with the Italian Grand Prix.
