Red Bull motorsports consultant Dr Helmut Marko says that the current TAG Heuer-badged engines provided by Renault mean the team can't aim for better than third in the championship.
The team scored a surprise victory in June when Daniel Ricciardo won the Azerbaijan Grand Prix.
However that was after setbacks for Mercedes pair Lewis Hamilton and Valtteri Bottas. A penalty also took Ferrari's Sebastian Vettel out of contention for the win.
Marko conceded that the rival teams usually have too much of a power advantage over Red Bull. He said 2017 was now about securing third place in the constructors championship.
"It [P3] is not good enough for Red Bull. But in our position with the engine it’s the best we can get," he told the official Formula 1 website.
Red Bull's junior team Toro Rosso is also reliant on Renault power. Currently in sixth place in the standings, it's only two points away from overhauling Williams.
"The aim was to finish fifth in the standings and I think that will be rather difficult," Marko admitted.
"Budapest turned in our favour, but from Spa on you will see the Mercedes-powered cars showing us their rear.
"We had a lot of possibilities in the first half of the season that we haven’t taken," he added. "Incidents with the drivers like in Silverstone are unfortunate, as are the reliability issues.
"A shame," he sighed.
Toro Rosso has also been affected by ongoing rumours about driver Carlos Sainz seeking to leave the team.
"Rumours! Typical summer-slump rumours!" laughed Marko, batting aside any such gossip. "You will see Carlos in a Toro Rosso in Spa ... The driver has a contract with us."
When it comes to contracts, Marko is in the curious position of having two of his current drivers being themselves sons of successful motor racing drivers.
Max Verstappen receives counsel from former F1 star Jos, while Sainz can seek advice from his world rally championship-winning father Carlos Sr.
"We tell the fathers that we talk to our employee," responded Marko firmly, when asked if either parent had injected themselves into contract talks.