Cyril Abiteboul says Red Bull cannot blame Renault for their failure to feature in the title fight this season. Daniel Ricciardo and Max Verstappen are fifth and sixth respectively in the drivers' championship, while the team are 122 points adrift of leaders Mercedes in the constructors' standings.
Although Red Bull enjoyed three victories in the first nine races of 2018 - matching their tally from last year - a string of DNFs prior to the summer shutdown has deepened divisions once again between the team and their engine supplier.
Verstappen's MGU-K failed when he was running fourth in Hungary, prompting the Dutchman to threaten to blow his engine up, while team principal Christian Horner said Abiteboul would "come up with his excuses" after the race.
Indeed, the Frenchman explained that Red Bull's refusal to take on an updated version of the component may have contributed to Verstappen's retirement and Abiteboul is clear that Renault have delivered a power unit capable of helping Red Bull challenge.
Discussing the strength of the Renault power unit in comparison to Mercedes and Ferrari, Abiteboul told Auto Motor und Sport: "The engine is good enough to put a car in pole position, win races and fight for the title. Red Bull proves it.
"Without their problems, they would now be fully in the title fight. And only two of their problems had to do with the engine."
Red Bull will switch to a deal with Honda in 2019, leaving just the works team and McLaren running with the Renault engine on the grid.
The British team do not offer quite the same benchmark as Red Bull have owing to their own aerodynamic struggles, but Abiteboul is confident that further gains will be made in Viry next season, when pressure will be ratcheted up by Ricciardo's arrival from Red Bull.
He added: "Here we are on schedule with our catching up. I am convinced that we will catch up with Mercedes and Ferrari in 2019, maybe even overtake.
"I am satisfied with the performance increase. Not yet with reliability.
"On the chassis side we are still lagging aerodynamically."