Alain Prost's parting shot at the Renault-owned Alpine team that he is leaving is to reveal a "reliability problem" with the new engine for 2022.
Alpine, based in Enstone (UK) and Viry (France), is pinning its hopes on a significant power unit re-design to close a reported 30-plus horsepower gap to the front-running engines.
Quadruple world champion Prost told L'Equipe: "There is a small reliability problem in the 2022 engine.
"During the simulations on the test bench, they have discovered that the power unit is still not working at the desired level," the F1 legend added.
Until now, Renault has been developing a version of the same basic power unit architecture for the past three years.
Renault CEO Luca de Meo said recently of the 2022 engine: "It is smaller, lighter and with a better centre of gravity, which will leave room to improve the aerodynamics."
Prost continued: "It is an ambitious project. There is also the question of performance, which will only be known when the car is on the track."