"Loic has been a really loyal and important member of the team for a number of years," he told reporters. "We had an internal reorganisation...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. I think he's going somewhere else at the end of the year."
Media speculation has indicated Ferrari, who have been wrestling with the aerodynamics on their 2012 car, as a likely destination for the Frenchman who helped Brawn win the 2009 constructors' title.
Brawn said former BAR and Red Bull technical director Geoff Willis was now in charge of the Mercedes aerodynamics group.