Helmut Marko, the former BRM F1 driver who is the trusted right-hand man and close advisor to Red Bull boss Dietrich Mateschitz, has delivered a withering critique of former Scuderia Toro Rosso team drivers Sébastien Buemi and Jaime Alguersuari.
The two racers were replaced at the end of last season by new youngsters Daniel Ricciardo and Jean-Eric Vergne.
"Toro Rosso was created to give young drivers a chance," Marko told Italy's Gazzetta dello Sport. "Alguersuari and Buemi had it for three years and after this time it's possible to evaluate a driver's development.
"We haven't seen in them any possibility of growth. Both are worthy of grand prix racing, but for us that's not enough: we need winners."
Buemi and Alguersuari had driven for Red Bull's junior Formula 1 team since the start and middle of the 2009 season respectively, but have been dropped in favour of the two newcomers for 2012.
Although Alguersuari's future is currently uncertain, Buemi will remain in the Red Bull fold as a reserve driver, ready to step forward to stand-in for Sebastian Vettel or Mark Webber should the needs arise.