Mercedes hasn't managed 2019 F1 updates as 'optimally' as possible

Wolff said a switch of focus to 2020 has prompted a slow down in development, although there will be new parts at the next race in Suzuka.

Asked if recent results are due to Ferrari improving or Mercedes - which claimed its first win since the summer break at Sochi last weekend, though only after Ferrari had led - underperforming, Wolff said: "I think the truth will be somewhere in the middle.

"I think they have and continue to make big steps in straightline performance, and they have had a good car in Singapore, a very good car in Sochi.

"If you put these dots together you are setting the benchmark. And this is what they did this last two weekends.

"In the same time, we haven't brought upgrades since a long time onto the car, and we probably haven't managed things as optimum as you can manage.

"But also we've been a bit unlucky also with our calls, and in the last few races we could have won some of these races, and we didn't. And that bad luck turned into good luck [in Sochi]."

Wolff said the lack of recent updates was a strategic decision.

"You've got to manage your resource in the right way, also looking into next year," he said.

"That is something which we consider very carefully.

"There will be a little thing in Suzuka, that we are just interested to explore. But not the big steps that we had when we pushed very hard until the summer."

Asked if that exploration was aimed at 2020, he added: "As the regulations stay the same it's all part of the same thinking."

This year's Mercedes has been characterised as a significantly more 'draggy' car than the Ferrari, but Wolff said changing philosophy was not a main focus of future development.

"It's something we're looking at, but you need to put it into perspective," he said.

"Between a draggy car and a not draggy car, probably the two extremes you see on track, on the whole grid you will find two-tenths difference.

"This is what you can extract in putting lots of bits on the car, versus having a streamlined car. So it has not such a big effect.

"It has an affect, but it's not the main effect."