Speaking to Red Bull's in-house Servus TV network, the always-blunt Austrian admitted the reigning world champion team is months behind its rivals.
"The season opener is coming at least two months too early for us," Marko said on the Sport und Talk programme.
"We are not where we should be."
He said the biggest problem is that in the 12 days of pre-Melbourne testing in Spain and Bahrain, Red Bull turned significantly fewer laps than any other traditional rival.
"This is a very, very serious thing," said Marko.
"At the moment we do not know what (time) period we will need to catch up, or whether we will at all," he admitted.
However, it may not be all bad for Red Bull, as even pacesetters Mercedes are expecting reliability - not speed - to be perhaps the most important factor next weekend in Australia.
"I believe that half the field will not finish," said team chairman Niki Lauda, "simply because there has not been the opportunity for enough testing."
But, unfortunately for Red Bull, the Renault-powered RB10 is not just unreliable.
"The Red Bull does not look good," an experienced source, trackside in Bahrain last week, was quoted by Germany's Auto Motor und Sport.
"Nothing seemed right -- the coordination of engine, gears and setup did not fit together. Sebastian Vettel was always sliding and spinning his wheels, while the Williams was like on rails," he added.
The car is also significantly slower in a straight line than its Ferrari and Mercedes-powered rivals, and Renault is taking some of the blame for that.
"Melbourne will be an anxious weekend," admitted technical boss Rob White.
"I hope we can support our teams and drivers to explore the performance of the car and allow the race to deliver its sporting verdict."