Sebastien Loeb's Acropolis Rally lead is down to 10.2 seconds as Petter Solberg put on a charge in very wet conditions on Saturday afternoon.
Bigois has been at the team since its Honda days in 2007, but has elected to move on as the result of a restructuring of the technical department. Team principal Ross Brawn said technical director Geoff Willis is to assume a more senior role in aerodynamics, and other reshuffling of staff meant Bigois had to take on a revised position that he did not want.
"Loic has been a really important member of the team for a number of years but we have had an internal re-organization. Perhaps, with some of the restructuring we have done, it didn't fit in with what he was hoping to do, so he asked to be released from his contract and we released him," explained Brawn. "He is going somewhere else at the end of the year."
He added: "We wanted to move forward in the way we organized the aero group and Geoff Willis is in charge of that group now. We wanted to do things differently, and Lois did not want to do the new role that we proposed for him, so it was by mutual agreement."
Despite speculation that Bigois is to take a role in the wind tunnel department at Ferrari, the Italian team has insisted that no deal is in place with the Frenchman.