Williams has confirmed chief technical officer Paddy Lowe is to take a "leave of absence" from Formula 1 on the eve of the 2019 season.
Lowe, who joined Williams for a second spell in 2017 after overseeing three consecutive constructors' championship wins with Mercedes, was already under pressure heading into this season after the team finished bottom of last year's championship for the first time in their history. His first vehicle, the FW41 scored just seven points across the season in what was a disastrous year.
Williams also announced on Wednesday that they should have both cars ready for Melbourne.
But a spokesperson for the team said that Rowe will be "taking a leave of absence from the business for personal reasons", in a message sent to a media WhatsApp group.
Lowe stressed during testing that he did not feel his job was under threat and urged Williams to remain as a unit, believing it will emerge stronger from its current setback.
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His departure comes after the team failed to complete its new FW42 chassis in time for it to participate in the start of testing.
No further information was supplied.
Lowe is a director at Williams but it is unclear whether he has a shareholding in the company.
But, one week before the F1 season begins in Australia, it has emerged that Lowe has stepped away from his role.