Mercedes boss Toto Wolff has admitted that his team have suffered a small "setback" in their 2019 engine plans.
Wolff said that the engine had not delivered the performance gains the team had have hoped for.
Mercedes will be gunning for their sixth successive world championship double next season; but with Ferrari and Red Bull putting up more of a battle this season, next season could prove more difficult for the Silver Arrows.
Speaking at a press conference for team sponsort Hewlett Packard Enterprise, Wolff gave the media an update on the progress of the 2019 car.
"These rules have been changed, normally the downforce should be less but the rumours you hear from the paddock is that people have been able to recuperate lots of that," Wolff said.
"There is a tremendous development race that is happening as we speak in finding downforce, reducing drag. And of course, the engine is a very important part, and adding more horsepower to the engine.
"So we are setting ourselves really ambitious targets. We have actually increased the targets six weeks ago because we heard some rumours the others were doing well, so we increased the final point for the first race where we need to be in absolute lap time. We are still on the slope.
"We've had some good weeks in the windtunnel, we've had a little bit of a setback on the engine side where we believed the new concept would deliver a little bit more."