Red Bull have placed a lot of stock in an engine upgrade expected to be delivered for the Italian Grand Prix, but Honda say it remains undecided when new parts will be delivered.
Dr Helmut Marko has suggested that Honda's fourth specification of engine could see Red Bull rival the qualifying modes of Mercedes and Ferrari, with it reportedly described as a "real boost" by the manufacturer..
Max Verstappen secured front-row starts in each of the two races immediately before F1's summer break, including his maiden pole position in Hungary.
Dr Marko has pushed Honda hard for more power already in 2019, but the Japanese marque's technical director Toyoharu Tanabe says the situation is not so simple.
"We are discussing all the time with the teams and we will decide when we apply a new engine or updated spec," he told Motorsport.com.
"At the moment no decision has been made yet. It depends on the situation and timing and the result of the discussions with the teams. It's very complicated."
Verstappen and new team-mate Alexander Albon will face engine penalties if new-spec parts are introduced, with their cars at the season-long limit for several components.
Despite Albon having not raced for Red Bull this year, engine penalties are attached to the car, not driver, so the Thai driver picks up Pierre Gasly's parts allocation, with the Frenchman doing likewise on Albon's car on his return to Toro Rosso.