Williams' beleaguered chief technical officer Paddy Lowe has left the team following their disappointing performance in pre-season testing.
Williams said Lowe was "taking a leave of absence from the business for personal reasons".
The move comes after the team failed to have their car ready for the start of the Barcelona tests.
It was also slowest of all when it did run after missing two and a half of eight days of running.
Deputy team principal Claire Williams said at the time that she was was "not just disappointed" by the delay.
"It's embarrassing not bringing a race car to a circuit when everyone else has managed to do that, particularly a team like ours that has managed to bring a race car to testing for the past 40-odd years," she said.
Williams headed into 2019 hoping to make a step forward after the worst season in their history saw them finish last in the championship last year.
The result was tension between the team and Lowe during testing, and questions about his tenure.
Lowe said that he was not concerned about his future and said the car was "a huge step forward" in terms of its responsiveness to changes and behaviour on track.
But less than a week later, Lowe has left the team, not explaining his reasons.
The team were not able to say when he might return and the expectation is that he will not.
Lowe moved to Williams in 2017 after three years leading the technical side of Mercedes as they won consecutive titles in 2014, 2015 and 2016.
He was previously technical director of McLaren, where he oversaw Lewis Hamilton's first world title in 2008, leaving after a 2012 season in which the team won seven races.