Lewis Hamilton may have had some regrets already about his decision to join Mercedes next season, according to his McLaren Formula One team principal Martin Whitmarsh.
In an interview with the official Formula One Website the Briton also says Mexican, Sergio Perez, will feel a lot of pressure as Hamilton's replacement.
Hamilton, the 2008 world champion is replacing retiring seven-times champion Michael Schumacher at Mercedes.
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 says it will be an emotional farewell with Hamilton after the last race of the season in Brazil later this month.
The team boss says he hopes Hamilton realises he's made a mistake by going to Mercedes but says he has to live with his decison.
Perez will be joining 2009 world champion Jenson Button at McLaren and Whitmarsh expects the 22-year-old will arrive with all sorts of pressure that he can't imagine right now.