Sam Michael is in Abu Dhabi making his first appearance with McLaren.
The Australian's last race as Williams' technical director was Korea, and it was expected that he would sit out the rest of the season on 'gardening leave' before starting his new job as McLaren's sporting director in 2012.
But Michael has been spotted in the McLaren garage on Friday, the British broadcaster BBC reports.
The report said Williams has "allowed" Michael to start work two races early, but not in official team gear. Indeed, the 40-year-old is wearing a plain white shirt.
He will ultimately have "responsibility for the development and management of the team's trackside operations", McLaren said earlier this season.
Williams' new technical director is Mike Coughlan, the sacked McLaren 'spygate' designer.