Mar.15 (GMM) McLaren on Friday admitted it is now "worried" about the pace of the new MP4-28 car.
Jenson Button was just ninth in opening practice in Melbourne, before lagging more than two seconds off the pace in the second ninety minute session.
Team newcomer Sergio Perez was consistently even slower.
"I think we should be worried about the pace," team boss Martin Whitmarsh told British broadcaster Sky.
While most top teams - notably continuing pacesetters Red Bull - simply evolved their 2012 cars for the final season of V8 regulations, McLaren unveiled a radical new car for this year, including novel pull-rod front suspension.
"I think we are still learning and there is a lot we still need to learn about this car," Whitmarsh added, "but we have struggled frankly to quite understand how it is performing."
Sporting director Sam Michael likened McLaren's new struggles to Ferrari's of early last year, when Fernando Alonso would ultimately go on to challenge for the title.
"By the fourth or fifth race they were there," he said.