Jenson Button and new team-mate Sergio Perez both endured up-and-down days during testing in recent weeks in McLaren's latest challenger, the MP4-28.
It was not until last Friday that Button enjoyed his best testing day and with it a belief he was finally beginning to understand a car that had been difficult to read up until then.
Ahead of the season-opening race in Australia in nine days' time, Whitmarsh concedes the team have gone out on a limb with the car, which in turn may result in time being needed to extract its full performance.
"We've faced a challenging few weeks prepping our new car for the 2013 season," said Whitmarsh.
"It's important to remember it is a new and uncompromising design we intend to develop aggressively throughout the year.
"Undoubtedly, it has great potential, and we fly to Melbourne determined to show well and to score points that should establish us in good stead for the drivers' and constructors' world championships.
"We're still working tirelessly to bring more pace to the car's performance envelope, and I believe we'll arrive in Australia in decent shape.
"I have great confidence our design, development and engineering teams will work tirelessly to shave tenths off its lap-times for Melbourne, and for Sao Paulo, and for everywhere in between."
The feeling is McLaren currently lag behind their main rivals in Red Bull and Ferrari, potentially even Mercedes and Lotus.
Whitmarsh, however, is convinced there is not one single person in F1 who could today say with any uncertainty the pecking order at the top, especially given the inclement weather throughout testing.
Whitmarsh added: "The often cold and sometimes wet conditions we experienced during pre-season testing in Barcelona and Jerez made it difficult to operate the tyres consistently within their optimal performance window.
"That issue, combined with a handful of typical testing setbacks, gave us a few headaches, but as ever our engineers and mechanics did extremely well to complete as much useful running as they did.
"But it was much the same for all the teams. As a result, anyone who says they already know in what order the cars will line up on the Albert Park starting grid on Sunday March 17 is a soothsayer of rare ability.
"Indeed, in truth, even after qualifying on Saturday March 16, no team principal will be genuinely confident of his car's race-spec performance relative to that of his principal opposition until the flag drops and the proverbial stops."
Despite the issues encountered by McLaren in pre-season, Whitmarsh is naturally exuberant with regards to the new campaign.
"In the days leading up to the Australian Grand Prix it's fair to say every team member of every team is looking over the precipice, balancing their hopes and fears, their nerves tensed in anticipation for the long slog ahead," said Whitmarsh.
"It's a tantalising prospect, and it's one that keeps everyone who loves our sport coming back for more."