Cape Town - Mercedes boss Toto Wolff has said the team have suffered a "setback" as their new engine concept has not delivered as expected.
In 2019, the Silver Arrows will be looking to clinch a sixth consecutive World Championship double, but team principal Wolff has said the preparation has not been all plain sailing so far.
"We’ve had some good weeks in the wind tunnel," Wolff said at a sponsor event with Hewlett-Packard.
"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.
"But these guys are very ambitious like all of us and so I’m optimistic.
"We will know when the first qualifying session gets underway in Melbourne, this is the moment where everybody shows their cards."
Although it appears that Formula 1 is in sleep mode, Wolff said that is far from the case and they have been forced even more into action with the fast development of other cars on the 2019 grid.
"There is a tremendous development race that is happened as we speak," he added.
"Finding downforce, reducing drag and of course the engine is a very important part, 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 that others were doing well."