Martin Whitmarsh has admitted McLaren are "undoubtedly struggling" two days before the Formula One campaign starts in earnest.
Following the opening two 90-minute practice sessions for Sunday's Australian Grand Prix, McLaren duo Jenson Button and Sergio Perez found themselves languishing down in 11th and 13th positions.
The Woking-based marque opted for a comprehensive redesign of their car over the winter, despite the stability in the regulations.
The belief was they would hit the ground running and from there be able to continually develop the car to keep it ahead of the pack.
The problem is, McLaren are not keeping up with their four main rivals in Red Bull, Ferrari, Lotus and Mercedes - instead finding themselves in the midfield alongside Sauber and Force India.
Team principal Whitmarsh said: "We took the decision to make quite a lot of changes, and we were hoping to get on top of them before the first race.
"As of today we are undoubtedly struggling. We are working through it over the course of this weekend."
Out in front at the end of both sessions at Melbourne's Albert Park was reigning triple world champion Sebastian Vettel in his Red Bull, with his fastest lap of one minute 25.908secs.
Not once at the end of his six days in the car in testing did Vettel finish top of the timesheet, but it is clear the latest creation of design guru Adrian Newey is again a title contender.
With the drivers turning to the fastest of the two Pirelli tyres available this weekend - the supersoft - over the second half of the second session, Vettel finished a quarter of a second up on team-mate Mark Webber.
Mercedes at least appear as if they can challenge the Red Bulls as Nico Rosberg and Lewis Hamilton were third and seventh quickest, although the closing stages of FP2 turned into a nightmare.
Rosberg, who finished just over four tenths of a second adrift of Vettel, pulled off track with a gearbox issue with four minutes remaining.
Three minutes prior to that Hamilton locked up at one stage before careering across the gravel and nudging his nose into a tyre wall, with the early suggestion being it was a car fault rather than driver error.
The 28-year-old, on his debut weekend for his new team, should have placed higher, but made another mistake earlier in the session on his one outing on the supersofts with a run across the grass.
Sandwiched in between the Mercedes pair were the Lotus duo of Kimi Raikkonen and Romain Grosjean as the team seek to prove last season was no flash in the pan when the Finn was third overall.
Ferrari are also in the hunt, with Fernando Alonso and Felipe Massa sandwiching Hamilton in sixth and eighth, with the latter within a second of Vettel.
Behind the top eight the rest were found wanting, with Force India's Adrian Sutil, on his return to F1 after a year on the sidelines, leading the way.
Sutil, though, was 1.5secs behind German compatriot Vettel, with Nico Hulkenberg on his maiden outing for Sauber completing the top 10, but over two seconds down.
Button finished 2.386s behind, followed by Paul Di Resta in his Force India, and then Perez, leaving McLaren staring at the prospect of not even qualifying in the top 10 tomorrow.
Of the five rookies in F1 this year, Sauber's Esteban Gutierrez was the pick down in 15th, with Williams' Valtteri Bottas 18th ahead of Marussia's Jules Bianchi.
Max Chilton finished 4.692s behind Vettel in 21st, whilst Geido van der Garde for Caterham again brought up the rear, losing an hour in FP2 after spinning into the gravel.