Lewis Hamilton was on course for an easy win at Abu Dhabi before a mechanical failure caused him to retire. Getty
In an interview with the official Formula One website (www.formula1.com), the Briton also said Mexican Sergio
Perez probably did not know what is about to hit him as Hamilton's replacement.
"I think he has on occasions, yes," said Whitmarsh when asked whether 2008 world champion Hamilton, who is replacing retiring seven-times champion Michael Schumacher at Mercedes, might have regretted his decision.
"Probably, when you make a decision you have to tell yourself that the decision is made so you have to look forward. You say okay, that it is in the past so you don't spend too much time thinking about why."
Mercedes have won one race, in China this year, since they took over the title-winning Brawn GP team at the end of 2009.
McLaren have won five grands prix this season alone and are the second most successful team in terms of wins in the history of the sport.
Whitmarsh said it would be an emotional farewell with Hamilton after the last race of the season in Brazil later this month and added that there had been some such moments already since the driver decided to leave.
"I hope he thinks today that he's made an awful mistake and I hope he thinks that next year. He's made that decision and he has to live with that decision," said the principal.
Perez is joining from Sauber, where he has had three podium finished this season but has also failed to score a point in the four races since his move was announced.
He will be joining 2009 world champion Jenson Button at McLaren and Whitmarsh expected the 22-year-old to learn everything he could from the older Briton.
"When Sergio gets to Australia (for the first race) in 2013 he will arrive with the kind of pressure that he can't imagine right now," said the team boss.
"At the first race, if he is not on the first two rows and fighting for a win the pressure will start to ramp. He doesn't know that yet."