But the British team announced on Thursday that Dennis is back as chief executive of the F1 division. The statement, making no mention of Whitmarsh, said further changes are looming.
Many have linked former Mercedes chief Ross Brawn with the Woking based team, who will switch to works Honda power for 2015 and beyond.
"Over the coming weeks I intend to undertake a thorough and objective review of each of our businesses with the intention of optimising every aspect of our existing operations," Dennis said on Thursday.
Dennis' return follows McLaren's dire 2013 season, and means Whitmarsh never succeeded in delivering a title as chief executive.