Ferrari and Toyota were the only two teams who travelled to Sakhir over the winter, spending six days testing in preparation for next week's race.
"Of course we would have liked to test in Bahrain but we do have to prioritise where we spend our time," Whitmarsh said in a team preview.
"Over the winter we have improved the aerodynamic efficiency of the car and cooling generally so it's not currently one of our vulnerable points.
"We have good data from running at the Bahrain track in previous years so we are confident it will not prove too much of a disadvantage."
McLaren are currently leading both championships after Lewis Hamilton won the season opener in Australia, although the team were unable to fight Ferrari in Malaysia.
Whitmarsh says the team are still working hard on the development of their car, and he revealed they are still evaluating if they will take new aero parts to Bahrain.
"The focus has been on reliability after the first two races which on the circuit have been pleasing but as always behind the scenes there are lots of things you need to attend to," he said.
"In particular the pitstops and the problem we experienced in Malaysia with Lewis' right front wheel. We have good pace in the car and need to maintain our momentum so obviously we have continued to develop the car in the wind tunnel.
"However we are still evaluating whether we will take some of the aerodynamic developments with us to Bahrain."
autosport.com